Dictionary term
Library
Also called software library · package
Web/DevBeginner
A collection of reusable code you call from your own program to do a specific job, while your code stays in control of the overall structure.
In plain English
Pre-written code you borrow for a specific job, so you don't have to write it yourself.
Analogy
Like a toolbox you reach into when you need a tool, versus a framework, which is the workshop layout itself.
Why it matters
Using a well-maintained library (for validation, dates, API clients) saves time and avoids bugs, but each one is a dependency you must keep updated.
In practice
React describes itself as "the library for web and native user interfaces"; you call it to render components, and Next.js is the framework around it.
Related terms
Sources
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