A cancellation (or cancel for short; French: "oblitération") is a postal marking applied on a postage stamp or postal stationery to deface the stamp and prevent its re-use. Cancellations come in a huge variety of designs, shapes, sizes and colors. Modern United States cancellations commonly include the date and post office location where the stamps were mailed, in addition to lines or bars designed to cover the stamp itself. The term "postal marking" sometimes is used to refer specifically to the part that contains the date and posting location, although the term often is used interchangeably with "cancellation." The portion of a cancellation that is designed to deface the stamp and does not contain writing is also called the "obliteration" or killer. Some stamps are issued pre-cancelled with a printed or stamped cancellation and do not need to have a cancellation added. Cancellations can affect the value of stamps to collectors, positively or negatively. The cancellations of some countries have been extensively studied by philatelists and many stamp collectors and postal history collectors collect cancellations in addition to the stamps themselves.