A liberal is someone on the left wing of politics — the opposite of a conservative. Also, a liberal attitude toward anything means more tolerance for change.
There are many meanings for liberal, but they mostly have to do with freedom and openness to change. A teacher with a liberal policy toward attendance is going to be forgiving of missed days. A bank with a liberal attitude toward your money would probably be bad: some things are awful if they're loose and free. But no one will give you a hard time if you use a liberal amount of catsup on your fries.