A question on special forces/green berets.

Before you think "This has been covered before", let me tell you this isn't the same as the other threads . I have a question...or a few.

First off, my uncle is a special forces (U.S.) green beret. Now, I was wondering is there a different between regular special forces, and green berets? Or are all special forces just called green berets? I know it sounds stupid, but I remember I asked him and I could swear that he said S.F. and green berets are the exact same thing. Before that, I always thought that Green Berets were a different division OF the special forces. The reason I'm asking is because his answer was kind of....vague I guess. I wasn't completely sure. I was just wondering if anyone could clear this up for me.