Reference

Glossary

Plain-English definitions for terms across PDF, image, audio/video, text, and developer tools.

A B C D E F G H J K L M P Q R S T U V W X Y

A

Alpha channel: An extra channel in an image file that stores transparency information. PNG and WebP support alpha; JPG does not. A pixel with 0% alpha is fully transparent; 100% is fully opaque. Required for logos and UI assets placed over coloured backgrounds. → PNG to JPG
ASCII: American Standard Code for Information Interchange. A 7-bit character encoding defining 128 characters (letters, digits, punctuation, control codes). The foundation of all modern text encodings; extended by UTF-8, which is backwards-compatible with ASCII for the first 128 code points.

B

Base64: An encoding scheme that converts binary data to a string of 64 printable ASCII characters (A–Z, a–z, 0–9, +, /). Used to safely embed binary content — images, certificates, credentials — in text-based formats like JSON, HTML, and email. Increases data size by ~33%. → Base64 Encoder
Bitrate: The number of bits per second used to encode audio or video. Higher bitrate means better quality and larger files. A 128 kbps MP3 is acceptable for podcasts; 320 kbps is considered near-lossless for music. Video bitrate is measured in megabits per second (Mbps).
Bookmark (PDF): A named destination within a PDF that appears in the document's outline panel. Allows readers to jump directly to chapters or sections. Different from hyperlinks — bookmarks are structural navigation aids, not web URLs.

C

camelCase: A naming convention where words are joined without spaces, with each word after the first capitalised: getUserName, fetchPageData. Common in JavaScript variables and function names. → Case Converter
Checksum: A short value computed from a larger block of data. Used to verify that data has not been corrupted or tampered with. MD5 and SHA-256 are common checksum algorithms — though MD5 is no longer considered cryptographically secure for security-sensitive applications. → Hash Generator
Codec: A coder-decoder algorithm used to compress and decompress audio or video data. H.264 (video) and AAC (audio) are the most widely supported codecs. H.265/HEVC offers better compression at the cost of computational complexity and licensing fees.
CMYK: Cyan, Magenta, Yellow, Key (Black). A subtractive colour model used in print. Mixing all four at 100% produces black. Unlike RGB, which adds light, CMYK works by subtracting wavelengths using ink. → Color Converter
Compression (lossy): A compression method that permanently discards data to achieve smaller file sizes. JPEG image compression and MP3 audio compression are lossy. The quality loss may be imperceptible at high quality settings but accumulates with each re-compression cycle.
Compression (lossless): A compression method that reduces file size without discarding any data. The original can be reconstructed exactly. PNG image compression, FLAC audio, and ZIP archiving are lossless. Typically produces larger files than lossy compression for the same content.
Cron expression: A five-field string that specifies a recurring schedule for automated tasks: minute, hour, day-of-month, month, day-of-week. "0 9 * * 1-5" means "9:00 AM Monday through Friday". Used in Unix systems, CI/CD pipelines, and cloud schedulers. → Cron Builder
CSV: Comma-Separated Values. A plain-text format for tabular data where each row is a line and columns are separated by commas (or another delimiter such as a semicolon or tab). Universally supported by spreadsheet applications and databases. → CSV to JSON

D

DPI (dots per inch): A measure of print or scan resolution. 72–96 DPI is standard for screens. 300 DPI is the minimum for professional print. Scanning documents at 300 DPI and saving as PDF produces large files — compress them afterwards.
Delimiter: A character that separates fields in a text-based data format. CSV typically uses commas; TSV uses tabs; some European locales use semicolons to avoid conflict with the comma as a decimal separator.

E

Encoding: The process of converting data from one representation to another. In text, encoding refers to the mapping of characters to binary values (UTF-8, ASCII). In media, it refers to compression (encoding video to H.264). In networking, Base64 encoding makes binary data safe for text channels.
EXIF: Exchangeable Image File Format. Metadata embedded in JPG, PNG, and HEIC files by cameras and smartphones. Contains camera model, lens, aperture, shutter speed, ISO, GPS coordinates, and timestamp. Strip EXIF before sharing photos publicly to protect location privacy. → Strip Image Metadata

F

Favicon: A small icon that represents a website in browser tabs, bookmarks, and mobile home screens. Typically 16×16, 32×32, or 48×48 pixels, stored as ICO, PNG, or SVG. Modern best practice is to provide multiple PNG sizes and a 180×180 Apple Touch Icon. → Favicon Generator
Flesch-Kincaid: A family of readability formulas that estimate the grade level (FK Grade Level) or ease of reading (FK Reading Ease) of English text. The Reading Ease score ranges from 0 (very difficult) to 100 (very easy). Plain conversational English scores 60–70; academic papers often score below 30. → Readability Scorer
Font subsetting: The process of including only the glyphs actually used from a font file, rather than the full character set. Reduces embedded font size in PDFs from several hundred kilobytes to tens of kilobytes. Applied automatically by most PDF compressors.

G

GIF: Graphics Interchange Format. A raster format limited to 256 colours that supports animation. Once the only widely supported animated image format on the web; largely superseded by WebP (for animated images) and video for performance-sensitive contexts. → Video to GIF
GUID: Globally Unique Identifier. Synonymous with UUID. The term is more common in Microsoft ecosystems; UUID is used in most others. Both refer to a 128-bit identifier displayed as a 32-character hexadecimal string grouped with hyphens. → UUID Generator

H

Hash / Hash function: A function that maps input data of any size to a fixed-length output (the hash or digest). The same input always produces the same hash; any change to the input produces a completely different hash. Used to verify file integrity, store passwords securely, and create digital signatures. → Hash Generator
HEIC: High Efficiency Image Container. Apple's default photo format since iOS 11, based on HEVC compression. Stores photos at half the file size of JPEG with equivalent quality. Poor compatibility with non-Apple platforms — convert to JPG before sharing broadly. → HEIC to JPG
HEX colour: A six-digit hexadecimal representation of a colour in RGB space. #RRGGBB, where each pair (RR, GG, BB) is a value from 00 to FF. #000000 is black; #ffffff is white; #005f9c is the ToolsHub brand blue. → Color Converter
HSL: Hue, Saturation, Lightness. An alternative representation of RGB colours designed to match human intuition. Hue is a degree on the colour wheel (0 = red, 120 = green, 240 = blue). Saturation is 0–100% (grey to full colour). Lightness is 0–100% (black to white). → Color Converter

J

JPG / JPEG: Joint Photographic Experts Group. A lossy raster image format optimised for photographic content. Achieves high compression ratios for photos by exploiting the human eye's reduced sensitivity to high-frequency detail in colour channels. Does not support transparency.
JSON: JavaScript Object Notation. A lightweight, human-readable data interchange format using key-value pairs, arrays, strings, numbers, booleans, and null. The de-facto standard for web APIs. Strictly typed — keys must be strings, and trailing commas are not allowed. → JSON Formatter
JWT: JSON Web Token. A compact, self-contained token format for transmitting claims between parties. Consists of three Base64url-encoded parts: header (algorithm), payload (claims), and signature. Commonly used for stateless API authentication. → JWT Decoder

K

Kbps / Mbps: Kilobits per second / Megabits per second. Units of bitrate for audio and video. Note: 1 kilobyte = 8 kilobits. A 128 kbps audio file uses 128,000 bits per second — about 16 kilobytes per second, or roughly 1 MB per minute.

L

Lossless compression: See Compression (lossless).
Lossy compression: See Compression (lossy).

M

Markdown: A lightweight markup language that uses plain text formatting syntax (# for headings, ** for bold, ` for code) and converts to HTML. Widely used in README files, documentation systems, and content platforms like Ghost and Notion. → Markdown to HTML
MD5: Message Digest Algorithm 5. A hash function producing a 128-bit digest. Fast and widely used for checksums. Not suitable for password hashing or security applications because it is vulnerable to collision attacks. Use SHA-256 or SHA-512 for security-sensitive uses. → Hash Generator
MIME type: Multipurpose Internet Mail Extensions type. A two-part label (type/subtype) that identifies the nature of a file. image/jpeg, application/json, text/csv, audio/mpeg. Used by browsers, servers, and APIs to determine how to handle a file.
MP3: MPEG-1 Audio Layer III. A lossy audio compression format. The most widely supported audio format across devices and platforms. Typical quality levels: 128 kbps (streaming), 192 kbps (general use), 320 kbps (near-lossless). → WAV to MP3

P

PDF: Portable Document Format. A file format that presents documents in a fixed layout, independent of software, hardware, or operating system. Created by Adobe in 1992; now an open ISO standard (ISO 32000). Supports text, raster images, vector graphics, embedded fonts, hyperlinks, encryption, and forms.
PDF/A: An ISO-standardised subset of PDF designed for long-term archival. Prohibits features that depend on external resources (embedded audio/video, external fonts, JavaScript). Used for legal, government, and regulatory document storage.
PNG: Portable Network Graphics. A lossless raster image format supporting 8-bit (256-colour), 24-bit (true colour), and 32-bit (true colour with alpha) modes. The de-facto standard for screenshots, UI assets, and images requiring transparency. Does not support animation (use WebP or GIF for that). → JPG to PNG
Percent-encoding: Also called URL encoding. A mechanism for encoding special characters in URLs as a percent sign followed by two hexadecimal digits. A space becomes %20; an ampersand becomes %26. Required because URLs can only contain a limited set of ASCII characters. → URL Encoder

Q

QR code: Quick Response code. A two-dimensional barcode that encodes text data (typically a URL) in a matrix of black and white squares. Readable by smartphone cameras without a dedicated scanner app. Error correction allows codes to remain readable even when partially damaged. → QR Code Generator

R

Regex: Regular Expression. A sequence of characters that defines a search pattern. Regex can match, extract, and replace text with extraordinary precision. The pattern \b[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,}\b matches email addresses. Most programming languages include a regex engine. → Regex Tester
RGB: Red, Green, Blue. An additive colour model where colours are created by combining red, green, and blue light at different intensities (0–255). Used by all digital displays. rgb(0, 95, 156) is the ToolsHub brand blue. → Color Converter
Raster image: An image represented as a grid of pixels, each storing colour information. JPG, PNG, WebP, and GIF are raster formats. Resolution-dependent: scaling a raster image up introduces pixelation. Compare with vector images (SVG).

S

SHA-256: Secure Hash Algorithm 256-bit. A cryptographic hash function producing a 256-bit digest. Considered cryptographically secure and widely used for file integrity verification, digital signatures, and password hashing (typically via bcrypt or Argon2, not raw SHA-256). → Hash Generator
snake_case: A naming convention where words are joined by underscores and all letters are lowercase: user_id, created_at. Conventional in Python variable names, database column names, and file systems that are case-insensitive. → Case Converter
SVG: Scalable Vector Graphics. An XML-based format for two-dimensional vector graphics. Resolution-independent: an SVG renders crisp at any size because it describes shapes mathematically. Supports animation, CSS styling, and JavaScript interaction. Not suitable for photographs. → SVG to PNG

T

Token (JWT): See JWT. In the context of authentication, a token is a self-contained credential that proves the holder's identity and permissions without requiring a server-side session lookup.

U

URL encoding: See Percent-encoding. → URL Encoder
UTF-8: A variable-width character encoding for Unicode. Backwards-compatible with ASCII for the first 128 code points; uses 1–4 bytes per character for the full Unicode range. The dominant encoding for web pages and APIs. Documents should declare their encoding explicitly (typically in HTML meta tags or HTTP headers).
UUID: Universally Unique Identifier. A 128-bit identifier formatted as 32 hexadecimal digits in five groups: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx. Version 4 (UUID v4) generates values using cryptographically secure random numbers, making collisions statistically impossible in practice. → UUID Generator

V

Vector image: An image defined by mathematical descriptions of shapes (paths, curves, polygons) rather than a grid of pixels. Scales to any resolution without loss of quality. SVG is the standard web vector format. Compare with raster images (JPG, PNG).

W

WAV: Waveform Audio File Format. A lossless, uncompressed audio container format. High quality but large file sizes — a minute of 44.1 kHz stereo audio is approximately 10 MB. The standard format for professional audio editing. → MP3 to WAV
WebP: A modern image format developed by Google supporting lossy compression, lossless compression, alpha transparency, and animation. Typically 25–35% smaller than equivalent JPG or PNG. Supported by all major browsers since 2020. → Convert to WebP

X

XLSX: The default file format for Microsoft Excel workbooks since Office 2007. An XML-based format stored in a ZIP archive. Open specification; readable by many non-Microsoft applications. The plain-text equivalent for tabular data is CSV. → Excel to CSV

Y

YAML: YAML Ain't Markup Language. A human-readable data serialisation format using indentation to represent structure. Commonly used for configuration files (Docker Compose, Kubernetes, GitHub Actions). A strict superset of JSON — all valid JSON is valid YAML. → YAML to JSON