Wiktionary
lock key
n. Any of certain keys of a computer keyboard that switch between certain states and are represented by LEDs.
Wikipedia
Lock key
LOCK is a function that locks part of a keyboard keys into a distinct mode of operation, depending on the lock settings selected.
Usage examples of "lock key".
Ellwood checked the message on the screen for correct addresses and then put the EncryptionLok-3 back inside its housing and pushed the Lock key on the touch-screen computer monitor.
He punched the door-lock key, started up, lifted onto the air-cushion and headed west into the desert.
He pressed the lock key on the phone and got a connection to Rankin.