Any pass that is not in a forward direction-even a pass parallel to the line of scrimmage-is considered to be a backward pass. Once a backward pass strikes the ground, it is considered to be a live ball and can be recovered by any player on the field.
One of the most famous instances of the backward pass rule was on January 8, 2000, in the 'Music City Miracle' between the Tennesse Titans and Buffalo Bills. Frank Wycheck threw a lateral across the field to Kevin Dyson, who then ran the ball 75 yards for the game-winning touchdown with time nearly expired. The play was reviewed extensively by video replay, but it was determined that the ball in fact did not travel forward, and the touchdown was good.