The top (horizontal) bar of the hockey net that sits 4 feet off the ice and is 6 feet in length.
If a puck hits the two outside metal bars of the net, it's often said, "The puck hit the post." However, if a puck strikes the top bar, "The puck hit the crossbar."
The crossbar is also used when a player bats the puck out of the air and into the net, to determine if the goal was legally batted in. A player must keep the stick below the crossbar when directing or deflecting a puck into the net.
The league continues to tinker with ideas to tweak the goal nets by either making them bigger, or even curving the crossbar to possibly increase scoring.