A codebase (or code base) is a collection of source code that is maintained as a unit. Typically, it can be used to build one or more software components including applications and libraries.
A codebase is typically stored in a source control repository of a version control system. A repository can contain build-generated files (which are therefore not source code), but typically such files are excluded from a repository, and therefore the codebase. A repository may contain data files (such as configuration) that are required for building or running the resulting software. But version control is not a required aspect of a codebase. Even the Linux kernel was maintained without version control for many years.