K - prefix letter used by KCS Industries in front of the plate number on its modern stamp production.

Kansas City Roulettes - improvised perforations applied by roulette to imperforate 1¢ and 2¢ postage stamps (Scott 408 and 409) by the postmaster of Kansas City in 1914 and 1915.

*Kansas-Nebraska Overprints - Series of 1922 postage stamps overprinted "Kans." or "Nebr." in 1929 for sale in those states, but valid in all states.  Scott 658-679.

KCS Industries - private printer and finisher of postage stamps.  Example: non-denominated Tulip booklet of 1991 (Scott 2520).

Killer Cancel - a cancellation that is very heavy, obliterating most of the design of a stamp.

Knife - 1) the pattern used to cut an envelope from a sheet of paper.  2) the device that cuts stamps apart as they are fed through an affixing machine.