Git fetch origin vs git fetch --all

Your repository may have one remote point known by alias as 'origin', but you may also have other remotes configured. The latter command would fetch from them all.

More in the docs for fetch.

git fetch --all

--all
Fetch all remotes.

If you want to get all the data and on the same time also to remove the
deleted data add the --prune flag

# Fetch all data, remove dangling objects and pack you repository
git fetch --all --prune=now

git fetch origin fetch data only from origin, and git fetch --all fetch data from all remotes (origin is one of them)