Defencemen

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.

Organized play of ice hockey originates from the first indoor game in Montreal in 1875. In subsequent years, the players per side were reduced to seven per side. Positions were standardized, and two correspond to the two defencemen of current six-man rules. These were designated as cover point and point, although they lined up behind the center and the rover, unlike today. Decades later, defencemen were standardized into playing left and right sides of the ice.

According to one of the earliest books on ice hockey, Farrell's Hockey: Canada's Royal Winter Game (1899), Mike Grant of the Montreal Victorias, describes the point as "essentially defensive. He should not stray too far from his place, because oftentimes he is practically a second goal-minder ... although he should remain close to his goal-keeper, he should never obstruct that man's view of the puck. He should, as a rule, avoid rushing up the ice, but if he has a good opening for such a play he should give the puck to one of the forwards on the first opportunity and then hasten back to his position, which has been occupied, in the interim, by the cover-point."

...
Wikipedia