What's the difference between "squash" and "fixup" in Git/Git Extension?

I've been using Git Extensions for a while now (it's awesome!) but I haven't found a simple answer to the following:

Sometimes, when typing a commit message, a make a typo. My friend showed me how to fix it the following way (in Git Extentions):

Right-Click on the commit > Advanced > Fixup commit

Then I simply check the box "Amend" and rewrite my message and voila! My commit message is fixed.

However this other option "Squash commit"... I have always wondered what it does?!

My question is:

Would someone simply explain me what is the exact difference between Squash commit and Fixup commit in Git/Git Extentions? They look kind of... "similar" to me:

I do not know what Git Extensions does with it specifically, but git rebase has an option to automatically squash or fixup commits with squash! or fixup! prefixes, respectively:

   --autosquash, --no-autosquash
       When the commit log message begins with "squash! ..." (or "fixup!
       ..."), and there is a commit whose title begins with the same ...,
       automatically modify the todo list of rebase -i so that the commit
       marked for squashing comes right after the commit to be modified,
       and change the action of the moved commit from pick to squash (or
       fixup).

The difference between squash and fixup is that during the rebase, the squash operation will prompt you to combine the messages of the original and the squash commit, whereas the fixup operation will keep the original message and discard the message from the fixup commit.