What is a "sandbox" in the context of cabal?

I saw cabal sandboxed mentioned multiple times when googling about cabal, mostly on SO or reddit.

Since I haven't seen that term in the cabal docs, I thought maybe it is something from the older cabal, or maybe I just missed it.

I then searched for "sandbox" in https://cabal.readthedocs.io/, and it found 3 occurences (https://cabal.readthedocs.io/en/latest/search.html?q=sandbox&check_keywords=yes&area=default), however all of them just mention sandbox as if it is understood what it means and what it is, and there is no explanation as to what is actually a sandbox in the context of cabal.

I am guessing that sandbox as a feature doesn't exist anymore and the parts of the docs that mention it need to be updated to not mention it anymore? Or are we supposed to understand what sandbox means but it isn't in the current version of the docs?

Thanks!

Start with the three occurrences found by searching for “sandbox” in the current Cabal documentation at https://cabal.readthedocs.io/. Determine whether Cabal still supports sandboxes and whether the existing references need explanation or removal; done means the documentation clearly defines the term or no longer presents it without context.

Written by the indexing model from the issue text.