[dodobirdlord]

It's easy to use a monorepo in a way that feels like a multirepo, and vice versa. I'm inclined to say that the defining difference is around versioning. To put it another way, can you choose to ignore that your dependencies have upgraded?

In a monorepo your builds are at the same point in time horizontally across all of your dependencies. You build together or not at all (though not necessarily at HEAD). In a multirepo you have the option to build against any (or some subset of) point-in-time snapshots of your dependencies on a dependency-by-dependency basis.

If you have a single monorepo that all of the code is in, but your build system allows you to specify what commit to build your dependency build targets at instead of forcing you to use the same commit as your changes, you actually have a multirepo. If you have a bunch of repos but you build them all together in a CI/CD pipeline that builds each at it's most recently released version then you actually have a monorepo.