(Ice) hockey: The wooden or fiberglass wall which surrounds the ice rink. The boards are around 42 inches high and are topped off by shatterproof plexiglass or equivalent material which protects the spectators from flying pucks, sticks, and players, but still affords a view of the play. In the modern era, the boards are typically festooned with advertisements — often for things hockey fans like such as beer, trucks, pizza, and beer, as well as the logos of the arena's name sponsor (banks and insurance companies, typically).
Variations in rink construction give the boards in different arenas unique characteristics. Some rinks have boards which deaden the puck and produce shallow rebounds. Others pinball the puck back into play at crazy angles, to the delight of forwards and the horror of goaltenders. The latter is more common in multi-purpose arenas where the boards go up and down frequently, to convert the place for Bon Jovi concerts and basketball games.
American sportscasters have taken to calling the boards "the wall" as in "Bourque throws the biscuit up the wall and out..." -- thankfully this has not caught on in Canada.