A line-out is Rugby union's equivalent of the throw-in in football (soccer). When a player puts the ball into touch (i.e. out of the field of play) it is the opposing team's line-out. An exception is that if the ball is kicked into touch from a penalty kick, the team that was awarded the penalty gets the line-out.
The hooker of the team whose line-out it is decides how many from each team are in the line-out. The forwards then line up in two rows. The forwards who are in the line-out stand five meters in from where the ball went to touch and one meter apart from the opposing forwards. The hooker must then throw the ball straight, directly in-between the teams as high as he likes. Members of the line-out are allowed to jump up and catch the ball or lift their teammates up to do so.