Like, as a embedded developer, these concepts are used pretty much every day. And in a good chunk of those, deallocation isn't allowed at all, so you can't say that the definition is around deallocation at once.
You can also see how glibc's malloc internally creates arenas, but that's not to deallocate at once, but instead to manage different locking semantics. https://sourceware.org/glibc/wiki/MallocInternals
There are implementations of arenas that, basically, act as separate memory managers. You can allocate and free memory inside them at will, but can also deallocate the whole thing in one sweep. The latter can be a lot faster, but of course, it requires you to know you can throw away all that memory in one go (handling web requests is the exemplar use case)
