A FC tag is the abbreviation or set of letters in '< >' brackets some players have at the end of their names - this identifies them as belonging to a Free Company or 'FC' (a FC is a player Guild), with the letters being an abbreviation for that FC's name (which is decided by the player who founded that FC). For instance, my character has the tag '<JZ>' at the end of her name, because that is the tag for 'JingZen', the FC I co-run with my boyfriend. Simple really.