Cutdown
A cutdown is a shortened version of a commercial. By omitting part of the commercial, such as by deleting one or two sentences, the length can be reduced. The audience is still reminded of the full message with the shorter spot.
The reason a cutdown is usually used is that the spot can then be broadcast more often for the same budget. Especially when a campaign is spread over several flights, a cutdown is usually chosen for the follow-up.