The Smash Back Room (formerly the Melee Back Room; also known as the SBR) is a protected forum on SmashBoards. Only members that have shown considerable knowledge or skill (either by posting intelligently or by tournament placement) are permitted to read and discuss in this forum. The Smash Back Room is most famous for producing a tier list every year or so. They also are well known for releasing suggested rule sets that tournament organizers often use in an effort to keep a standard play format across all regions.
While the Smash Back Room is often criticized for it's lack of openness and it's exclusivity, it is still the de facto "governing body" of most of the competitive smash community. The vast majority of tournament organizers (and almost all high level tournaments) use the SBR recommended rule sets and their tier list is by far held in the highest regard by the professional community.