Dependency

A dependency is an outside piece of software your project relies on to run, usually pulled in as a named package so you reuse that capability instead of writing it yourself.

A dependency is an outside piece of software your project relies on to run, usually pulled in as a named package so you reuse that capability instead of writing it yourself. The project keeps a list of these packages by name and version, and a tool installs them so the imported code is present wherever the project runs. Say you are building a to-do app and you want it to format dates as 'in 3 days' instead of a raw timestamp. Rather than write that calendar logic from scratch, you tell your assistant to add a date-formatting package; it gets added to the project's list, installed, and imported, and your code calls it directly.

Builder example

A manifest and lockfile help reproduce a dependency graph across environments. Compatibility ranges, platform-specific binaries, transitive packages, install scripts, registries, and runtime versions can still differ. Dependencies also add maintenance and supply-chain obligations beyond whether installation succeeds.

Common confusion: A dependency is code your project pulls in by name, while your own source files are code you wrote and maintain directly. Adding a package speeds up the build, and it also hands part of your app to an outside maintainer whose updates and security fixes you now depend on.