Character - the role a player assumes when playing the game
Session - a single block of time in which the players play the game (usually several hours long)
Campaign - a series of sessions that are played within the same game system and universe
Game Master - the player who assumes the responsibility of describing what happens as a result of the player characters' actions
Nonplayer character - a character within the game controlled by the Game Master rather than a player
Setting - the fictional world that an RPG takes place within
System - the rules that power a specific RPG
Numenera's setting feels like a mix of science fiction and fantasy. You play as a character living one billion years in Earth's future on the ruins of many previous civilizations. Fair warning: this setting is really really weird...