Core
Noun · Development
Definitions
The central or most essential part of a codebase, library, service, or processor around which other pieces are built. Calling something core usually means it has broad responsibility, many dependencies, or importance to overall system behavior.
In plain English: The central and most important part of a system.
Example: "They kept the parser small because it sat in the core of the toolchain and every plugin depended on its behavior staying stable."