Glossary
A developer glossary, written to teach — built to be cited.
1.4k terms across 32 categories — definitions, examples, common mistakes and fixes. Authored under one editorial standard. Cross-linked, searchable, and openly crawled by AI agents.
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Division by Zero & DivisionByZeroError 6
Undefined Array Key / Offset Errors 4
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HTML Meta Tags
Tags in <head> that provide page metadata — title, description, viewport, Open Graph — for browsers, search engines, and social platforms.
1mo ago
frontend beginner
Image Optimisation
Reducing image file size and delivery overhead through format choice (AVIF, WebP), compression, responsive sizing (srcset), lazy loading, and explicit dimensions — the single highest-impact performance lever for most websites.
1mo ago
performance intermediate
Largest Contentful Paint (LCP)
A Core Web Vital that measures when the largest above-fold content element (typically the hero image or main heading) becomes visible — target under 2.5 seconds. The most impactful page speed metric.
1mo ago
performance intermediate
Mixed Content (HTTP on HTTPS)
When an HTTPS page loads resources (images, scripts, stylesheets) over HTTP — browsers block active mixed content and warn on passive, undermining the security of the HTTPS connection.
CWE-319
1mo ago
security intermediate
Open Graph Protocol
Meta tags that control how a page appears when shared on social platforms — title, description, image, and URL shown in link previews on Facebook, LinkedIn, Slack, Discord, and Twitter/X.
1mo ago
frontend beginner
Resource Hints (preconnect, prefetch, preload)
HTML link attributes that instruct the browser to take early action on resources — opening connections, fetching future pages, or loading critical assets before they are discovered in HTML parsing.
1mo ago
performance intermediate
Script Loading (defer, async, type=module)
How and when browser downloads and executes JavaScript — defer, async, and type=module control whether scripts block HTML parsing and in what order they run.
1mo ago
frontend intermediate
Structured Data — JSON-LD
Machine-readable schema markup embedded in a <script type='application/ld+json'> block, enabling Google rich results — star ratings, FAQs, breadcrumbs, events, and recipes in search.
1mo ago
frontend intermediate
API Versioning
Strategies for evolving an API without breaking existing consumers — URI versioning, header versioning, and content negotiation.
1mo ago
api_design intermediate
CSS Cascade Layers (@layer)
CSS @layer lets you explicitly define the order in which style groups are applied in the cascade — styles in a later layer always win over earlier ones regardless of specificity, eliminating specificity wars in large codebases.
1mo ago
frontend intermediate
Docker HEALTHCHECK
A Dockerfile instruction that defines how Docker tests whether a container is healthy — enabling automatic restart and load balancer removal on failure.
1mo ago
devops intermediate
Git Rebase vs Merge
Merge preserves branch history with a merge commit — rebase rewrites commits onto the target branch for a linear history.
1mo ago
git intermediate
HTTP Content Negotiation
The HTTP mechanism by which clients declare what formats, languages, and encodings they accept (Accept, Accept-Language, Accept-Encoding) and servers respond with the best match — or 406 Not Acceptable if none fits.
1mo ago
api_design intermediate
HTTP/2 Server Push & Early Hints
HTTP/2 Server Push lets a server proactively send assets (CSS, JS, fonts) before the browser requests them. 103 Early Hints is its practical successor — sending Link preload headers before the full response is ready.
1mo ago
networking intermediate
InnoDB vs MyISAM
InnoDB is the default MySQL storage engine supporting transactions, foreign keys, and row-level locking — MyISAM is legacy with table-level locking and no transaction support.
1mo ago
database beginner
INSERT ... ON DUPLICATE KEY UPDATE PHP 5.1+
An atomic MySQL upsert — inserts a new row or updates the existing one if a unique key constraint would be violated.
1mo ago
database intermediate
Linux File Permissions
Read, write, and execute permissions assigned to owner, group, and others — the foundation of Linux access control for web application files.
CWE-732 OWASP A5:2021
1mo ago
linux beginner
7.5
Memory-Mapped Files
A file mapped directly into a process's virtual address space — reads and writes go through the OS page cache rather than read()/write() syscalls, enabling fast access to large files and shared memory between processes.
1mo ago
linux advanced
Mutex vs Semaphore PHP 7.0+
A mutex allows only one thread to access a resource at a time — a semaphore controls access to a pool of N identical resources.
CWE-362
1mo ago
concurrency advanced
MySQL AUTO_INCREMENT
A column attribute that automatically assigns sequential integer IDs on INSERT — the standard primary key pattern in MySQL.
1mo ago
database beginner