Hockey is a team sport played on an ice surface. The game is played on skates with sticks and a hard rubber disk called a "puck".
A team consists of at most 22 players, of whom at most six may be on ice at the same time. Usually one of the six is a goalkeeper or goalie. The other five players include three forwards and two defensemen. The foward positions are the left wing, center and right wing. Typically the same three forwards will play together as a "line". The defensemen typically stay together as a pair but may change less frequently than the forwards. Ice hockey is a fast paced game and player changes may happen every few minutes and often without an interruption in play.
The area of play is called a rink. The international rink is 200ft long and 100ft wide. The corners of the rink are rounded with a radius of 28ft. The rink is enclosed by boards that are between 3ft 4in and 4ft high.
The surface of the ice is broken up into different sections by lines painted beneath the ice surface. Goal lines are located 10 ft from each end of the rink. Goal lines extend across the width of the rink, are 2" wide and are painted red. Blue lines are located 60 ft from each end of the rink. The Blue lines extend across the width of the rink and continue up the boards. They are 12" wide and, obviously, are painted blue. The Centre Red line is a 12" wide red line located in the centre of the rink and extending across the width of the rink and up the boards.
One function of the blue line is to determine if the team with the puck is "offside". The play is offside if an offensive player crosses the blue line closest to the defending team's goal before the puck.
The game originated in Canada around 1900 or something...Actually, I believe it's origins are in Northern Europe.
At present the game is most popular in North America and North Europe. The premier league is the National Hockey League (NHL).