Truncation is the act or process of shortening something by cutting off part of it. It can also refer to the state of being shortened. To truncate means to shorten something by removing a portion of it. The verb to truncate means to cut or shorten.
You can truncate a board that is too long with an electric saw, a chainsaw, or even a karate kick. Less commonly, truncate can be used as an adjective with the same meaning as shortened, as if a part had been cut off.