Dependency
By Sitraka Forler · Lecturer, Durham Business SchoolUpdated 13 September 2026 About this site
A package, library or service that your code needs in order to run.
A dependency is something you rely on but did not build: in code, a package such as pandas, where direct dependencies are the ones you install and transitive dependencies are what those packages pull in. Record exact versions in requirements.txt or a lock file, or a fresh install may fetch a newer release that breaks your code. In IT operations, the word also means one system relying on another.
Example
# pandas becomes a direct dependency python3 -m pip install pandas # "Requires:" lists what pandas itself needs python3 -m pip show pandas # pin installed packages to their exact versions python3 -m pip freeze > requirements.txt # rebuild the same set on another machine python3 -m pip install -r requirements.txt