A power play in ice hockey is a term used to describe a situation where one of the opposition's players is serving a penalty. Most power plays are 5-on-4, though up to two players can serve a penalty at the same time, making for the very rare 5-on-3 power play. Power plays are fairly common in the NHL, and can be seen by each player's penalty minutes.
A power play goal is a goal scored by the team with a 1- or 2-man advantage.