Glossary — U
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UI (User Interface)
What the user sees and interacts with. Buttons, forms, layouts, colors — the entire visible surface of an app.
Unicode
The universal character-encoding standard that covers virtually every writing system in the world, plus emoji, plus a lot more. Each character has a code point. UTF-8 is the most common encoding of Unicode for files and the web.
See also: Text encodings & UTF-8
URL (Uniform Resource Locator)
The address of a resource on the web. https://stmarkbible.com/quiz?level=3 is a URL. Made of scheme (https://), host (stmarkbible.com), path (/quiz), and query (?level=3).
useEffect / useState (React)
The two most-used React hooks. useState gives a component a piece of state that survives re-renders and triggers a re-render when set: const [count, setCount] = useState(0). useEffect runs side effects after render: useEffect(() => { document.title = "..."; }, [count]) — the second argument is the dependency array; the effect re-runs when those change.
UTF-8
The dominant text encoding on the web — and in most other places. Backwards-compatible with ASCII (English letters use one byte each), but can encode any Unicode character using one to four bytes. If you ever see “café” instead of “café,” somewhere along the line a byte sequence was decoded with the wrong encoding.
See also: Unicode, Text encodings & UTF-8
UUID (Universally Unique Identifier)
A 128-bit ID, usually written as 32 hex characters in 5 groups separated by dashes: 550e8400-e29b-41d4-a716-446655440000. Generated randomly. The chance of two UUIDs colliding is astronomically small. Used as primary keys in databases, request IDs, session tokens — anywhere you need an ID that doesn’t reveal a sequence (unlike auto-incrementing integers).
See also: Key (database)
UX (User Experience)
The overall experience of using a product — how it feels, not just how it looks. Includes information architecture, flow, micro-interactions, loading states, error messages, copywriting. UI is part of UX, but UX is broader.
See also: Design & UX
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