In philately, the term cover pertains to the outside of an envelope or package with an address, typically with postage stamps that have been cancelled and is a term generally used among stamp and postal history collectors. The term does not include the contents of the letter or package, although they may add interest to the item if still present. Cover collecting plays an important role in postal history as many covers bear stamps, postmarks and other markings along with names and addresses all of which help to place a cover at a given time and place in history.
on-piece — в филателии вырезанный из цельной или целой вещи или почтового документа фрагмент прямоугольной, квадратной или другой формы, содержащий погашенные знаки почтовой оплаты, оттиски различных почтовых или других штемпелей и штампов (например, предварительного гашения).