If someone shows up as "Facebook user" in messages, does it mean that their account is deactivated or deleted? Or that they blocked me?

If an account still shows the user's name but it is black and cannot be clicked then one of you has blocked the other.

If the user's name is replaced by "Facebook User" then their account has been deactivated, suspended, or deleted.

If someone shows as "facebook user" it just means that person deleted or deactivated their account, so they are no longer on Facebook, their posts are all gone, all that exists is what you have in your messages. If someone blocked you, their name and profile would still be there, just you would not be able to respond.

This is a very tricky question because it depends on two things:

1. If the person picture is still there this means they blocked you. The picture doesn't disappear straightaway.
2. If their picture is blank from the first moment it said Facebook User, then they have blocked you.

I have a friend who loves to block me over little disagreements, then I have another friend who disables his account almost every week, aha. So I know the differences now.

If there is facebook user instead of a name it means that their account is deleted or deactivated.

If facebook has blocked the user you cannot type anything in the message box.

That happens when one of your friends blocked you and their name and photo removed then it shows you only as a "Facebook user" or the account is deleted or deactivated