The six players on each team are typically divided into three forwards, two defencemen, and a goaltender. The term "skaters" is typically used to describe all players who are not goaltenders. The "forward" positions consist of a "centre" and two "wingers": a "left wing" and a "right wing". Forwards often play together as units or "lines", with the same three forwards always playing together. The "defencemen" usually stay together as a pair generally divided between left and right. Left and right side wingers or defencemen are generally positioned as such, based on the side on which they carry their stick. A substitution of an entire unit at once is called a "line change". Teams typically employ alternate sets of forward lines and defensive pairings when "short-handed" or on a "power play". The goaltender stands in a, usually blue, semi-circle called the "crease" in the defensive zone keeping pucks from going in. Substitutions are permitted at any time during the game, although during a stoppage of play the home team is permitted the final change. When players are substituted during play, it is called changing "on the fly". A new NHL rule added in the 2005–06 season prevents a team from changing their line after they "ice" the puck.