What is "defenceman"

n. In ice hockey and lacrosse, a player position with a primary responsibility to prevent the opposing team from scoring goals; same as defender in many other ballgames.

Defence (defense in the USA) in ice hockey is a player position whose primary responsibility is to prevent the opposing team from scoring. They are often referred to as defencemen, D, D-men or blueliners (the latter a reference to the blue line in ice hockey which represents the boundary of the offensive zone; defencemen generally position themselves along the line to keep the puck in the zone). They were once called cover-point. A good defenceman is both strong in defensive and offensive play and for defenceman pairing also need to be good at defending and attacking

In regular play, two defencemen complement three forwards and a goaltender on the ice. Exceptions include overtime during the regular season and when a team is shorthanded (i.e. has been assessed a penalty), in which two defencemen are typically joined by only two forwards and a goaltender; in NHL play in overtime effective with the 2015-16 season the teams have only three position players and a goaltender on the ice and may use either two forwards and one defenceman (typically), or conversely, two defencemen and one forward.