Full Combo, more commonly abbreviated as FC, is the term that refers to beating a song while correctly playing every note without overstrumming. This is different from simply scoring 100% on a song, since one can "break" (reset) their Multiplier, by overstrumming, and still play 100% of the notes. Every single song in the entire series has been FC'd by at least one person, with the exception of Trogdor (NTSC). The NTSC version of Trogdor has been thought to be impossible due to the strumming speed of a part of the song exceeding the strum limit of the NTSC version of Guitar Hero II. As of now, there is no proof it has been FC'd, but no proof it cannot be FC'd either.
FBFC - also known as Full Band Full Combo, meaning that the maximum amount of people in a band (in a majority of cases, guitar, drums, bass, and vocals) FC a song without any duplicate instruments if the song does not include all four instruments.
OMBFC - One Man Band Full Combo, meaning that that each instrument has been FC'd by the same person.
FGFC - Full Game Full Combo, meaning that a player has FC'd every setlist song, not including DLC.
FSFC - Full Series Full Combo, meaning that a player has Full Game FC'd every game in the series. On guitar, no one has yet achieved a Full Series FC. However, bass, drums, and vocals have all been FSFC'd, albeit just once each for drums and vocals. The only person with a FSFC on vocals is parzrevenge44 and the only person with a FSFC on drums is smarock (BeastinIsMyGame). Several people have achieved a Full Series FC on bass. The people who are closest to a guitar FSFC are RobGHH (766/767 FCs) and UndeadFil13QC (766/767 FCs + an overstrum). Both players are missing just "I'm the One" by Van Halen to complete their Full Series FCs.