Two players on the ice and usually 6 or 7 on the roster, who play either left or right defense, whose primary responsibility is defending, as well as distributing the puck to the forwards to get it out of the zone.
Although the primary responsibility of a defenseman is defense, some of the defenseman considered the best of all time were also very offensive. Bobby Orr, Paul Coffey and Nicklas Lidstrom for example were touted as some of the best defensemen who could skate and score as well as play the position.
Orr is often considered the greatest defenseman of all time and the player who revolutionized the position to include an offensive repertoire, which we see in many of today's top d-men.
Defensemen usually battle in the corners and in front of their own net in the defending zone with the other team's forwards. They then usually reside near the blue line in the offensive zone. However, there are no rules about where they can go. Defenseman and forwards can interchange with each other, sometimes even on set plays, to try and confuse the other team.