Truncating is the act of shortening something by cutting off a portion of it. The verb truncate is used to describe this action. It can be used to describe physical objects, such as a board that is too long and needs to be cut down with an electric saw, a chainsaw, or even a karate kick. It can also be used to describe abstract concepts, such as a truncated version of a story or a truncated picnic caused by a sudden downpour.
The adjective truncated is used to describe something that has been shortened in this way.