offlineutils
10 terms
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Glossary

Plain-English definitions of every concept the offlineutils.com tools touch — what each one is, how it works, when to reach for it, and which tool on this site operates on it.

All glossary terms

Base64

aka Base-64, Base 64 encoding

Base64 is a way of encoding arbitrary binary data as a string of 64 ASCII characters (A–Z, a–z, 0–9, '+', '/') so it can travel through systems that only handle plain text — like email, URLs, JSON, or HTML data URIs.

Cron Expression

aka Crontab, Cron schedule, Cron pattern

A cron expression is a five-field string (or six fields with the Quartz seconds extension) that describes a recurring schedule — used by Unix cron, Kubernetes CronJobs, GitHub Actions schedules, and most modern job runners to say things like 'every 15 minutes' or 'every weekday at 9am'.

Cryptographic Hash

aka Hash function, Digest, Message digest, Checksum

A cryptographic hash function takes any input and produces a fixed-length pseudo-random output (the 'digest') that uniquely identifies the input — and is computationally infeasible to reverse, making hashes the foundation of integrity checks, content addressing, and password storage.

EXIF

aka Exchangeable Image File Format, EXIF metadata

EXIF (Exchangeable Image File Format) is the metadata standard cameras and phones embed inside JPEG photos — including GPS coordinates, camera model, capture timestamp, and shutter settings — which is why a holiday photo can quietly leak the exact street address it was taken at.

JSON

aka JavaScript Object Notation, RFC 8259 JSON

JSON (JavaScript Object Notation) is a lightweight text format for structured data — built from objects, arrays, strings, numbers, booleans, and null — that's become the lingua franca of web APIs, configuration files, and data interchange between services.

JSON Web Token

aka JWT, JOSE JWT, JSON Web Token (RFC 7519)

A JSON Web Token (JWT) is a compact, URL-safe credential made of three Base64URL-encoded segments — header, payload, and signature — that an API issues so a client can prove who it is on subsequent requests without re-authenticating each time.

OKLCH

aka OKLCH color space, oklch() CSS color function

OKLCH is a perceptually uniform color space — built on the OKLab perceptual model — that lets designers reason about colors using lightness, chroma, and hue values where equal numeric changes correspond to equal perceived changes. Modern CSS exposes it via the oklch() color function.

Regular Expression

aka Regex, Regexp, Pattern matching

A regular expression (regex) is a small pattern language for describing the shape of strings — used to validate input, search inside text, extract data, and substitute matches across virtually every modern programming language.

ULID

aka Universally Unique Lexicographically Sortable Identifier

A ULID (Universally Unique Lexicographically Sortable Identifier) is a 128-bit identifier encoded as 26 Crockford base32 characters that is sorted by time when generated, making it a drop-in replacement for UUID v4 with much better database insert performance.

UUID

aka Universally Unique Identifier, GUID, RFC 4122 UUID

A UUID (Universally Unique Identifier) is a 128-bit value, usually written as 32 hex digits in the canonical 8-4-4-4-12 grouping (e.g. '550e8400-e29b-41d4-a716-446655440000'), used as a globally unique ID that any computer can generate without coordination.