On piece

On piece - a stamp on sufficient of the original envelope or wrapper to show complete postmark, or other philatelic evidence of importance to prove authenticity - as in a bisect, for instance.
On piece ...

On piece: This is a used stamp (or stamps) still attached to part of the envelope or card it was used on.
On cover: A used stamp or stamps still affixed to the cover on which they were used.

On Piece: A stamp on a portion of the original envelope or wrapper showing all or most of the cancel; something less than an entire cover, on which a stamp is to be found.

On piece: A stamp on a part of an envelope preserved with the cancellation.
Original gum: gum that is present in mint stamps & not tampered with.
Oxidation: Darkening of the ink stamps when they come in contact with air and sunlight.

On Piece - A stamp including a portion of the original envelope which shows the cancel mark.
Ordinary Usage - Indicates the use of the correct rate of postage.

"On piece"
Philatelists use the term "on piece" to describe a cancelled stamp on a piece of paper, usually a corner cut from an envelope, and ideally including all of the postmark/cancellation. A stamp may also be "on cover", i.e.

Used on Piece Stamp retained on a portion of the original cover to preserve the entire postmark
Used Abroad Stamps of one country used and postmarked in another country.

A pound of stamps on pieces of paper may run to as many as four thousand stamps. Off paper a pound would run to considerably more.

collecting, you would do well to stay away from the great crush of new issues that is even now swamping collectors -- stamps issued by the USPS not included in the take-the-money-and-run list of issuers of dubious stamps -- and concentrate on pieces ...

Killer - A cancellation handstamp used to obliterate an adhesive and usually of so heavy a nature that it successfully "killed" the stamp to prevent re-use.
Kiloware - Unsorted modern material, typically postage stamps off paper or on piece, ...

See also: Stamp, Piece, Used, Local, Cancel