(n.) 1. A key with a large portion of the bit filed away so that it can open different locks. Also called passkey.
(n.) 2. A passkey with much of the bit filed away so that it can open different locks.

Source: Dictionary.com

(n.) Any non cylinder key whose bit, blade, and/or post is cut away enough to allow it to enter and turn in locks with different ward arrangements.

Source: Lock Industry Standards and Training (LIST) Council