The blocker consists of a glove with a rectangular board attached to the backhand side. The board is usually curved up at one end, which is designed to help control the deflection of the puck and will create a tougher angle on a shot if a goalie uses the shaft-down technique. The blocker is worn on the hand that holds the stick, so a right-handed goaltender will wear the blocker on the right hand, and a left-handed goalie will wear it on the left hand. This is called a "full right goalie" as the goaltender wears their catch glove in the right hand. A blocker is sometimes called a waffle in reference to older models, which were covered with real leather, but had holes cut in the leather to save weight, which gave the blocker a waffle-like appearance. The placement of the palm on the back of the blocker varies though it has been traditionally placed in the middle. Newer models tend to place the palm further to the inside of the glove in order cover more of the net. Typically, the goalie wears only one blocker. However, near the end of his career, retired goalie Dan Blackburn played with two blockers after nerve damage rendered him incapable of closing his glove hand.

More Info: en.wikipedia.org