Repository
also: repo, repos, repositories
A project's codebase stored together with a full history of every saved change. People usually shorten it to "repo".
A storage location for a project managed by a version control system such as Git. It holds the project's files plus a complete history of changes, and can be copied to other computers or hosted on services like GitHub.
A codebase is the current draft of a book. The repository is that draft plus every earlier version, with notes on who changed what, and when.
The history in a repository is your safety net. If an agent's change goes badly, that history lets you see exactly what changed and go back to a version that worked.
I don't see a repository here yet, so these changes aren't being tracked. Want me to set one up before I start editing?
Before making big changes, check that everything in the repository is saved, so we can go back if something breaks.
Thinking a repository and a codebase are the same thing. The codebase is the code. The repository also stores the history of how that code changed.