(n.) 1. A slot for a key in the hub or shaft of a wheel.
(n.) 2. The keyhole of a cylinder lock.

Source: Dictionary.com

(n.) 1. The opening in a lock or cylinder which is shaped to accept key bit or blade of a proper configuration.
(n.) 2. The exact cross sectional configuration of a keyway as viewed from the front. It is not necessarily the same as the key section.

Source: Lock Industry Standards and Training (LIST) Council