Cocoapods is a dependency manager for iOS and macOS that allows developers to reuse third-party open-source code (called pods) in their projects. It maintains a central repository (Trunk) of pods that can be added to a project by specifying them in a Podfile. Running pod install downloads and integrates the dependencies, keeping them up-to-date. Developers can also create their own pods and publish them to the Cocoapods repository for others to use in their projects.