Definition
Plain language
A way of plugging one code project into another as a linked copy.
As stated in the literature
A pinned reference from one Git repository to a commit in another, materialized as a nested checkout; a common vector for mixing private and public trees in the same working directory.
Also called: submodules
Why it matters: Submodules keep dependencies at known versions, but they also quietly place separate repositories — sometimes with very different privacy expectations — side by side in one working directory.
For example, a public open-source project can pin a specific version of a shared library as a submodule, so cloning the project also pulls that library into a nested folder.
Heard on the show
“The agent's task is to add a fork of a public library, as a submodule, and find where the user's private code diverges.”Episode 269 — How a Forged Transcript Got Model Weights Past a Safety Monitor