Professionally Speaking

When people talk about being "professional" - it's a word I don't really understand. I don't know what it means. I get it if something is effective, or innovative or, well done, or cool, or high quality - but I don't know what "professional" means. It sort of has a mildly negative connotation for me, now that I think of it. Corporate, stayed, distant, cold, how's it usually done - professional.