Envelopes with preprinted stamps that are sold by most post offices. One way that these are collected is by cutting a square corner off the envelope including the preprinted stamp with good margins. When both the front and back of the envelope are cut off, the item is called a full corner. If it is impractical to save the entire cover, full corners are preferred.
In philately, a cut square is a rectangular or square piece cut from postal stationery which includes all parts of the item's imprinted design related to postal uses, including any surcharges, postmarks or pre-cancels. It is distinguished from an 'entire' (the complete postal stationery item) or the more common practice of earlier eras of 'cutting to shape', or removing all the paper apart from the imprint design.