What is "f-lock"

The F-Lock key, introduced by Microsoft in 2001 toggles the state of the function keys. When on, keys F1 to F12 behave as applicable, with meanings defined by the application being used at the time. When off, new behaviour is used: F5 means "open", F10 means "spell" etc. In early models, the state reverted to off at each reboot or keyboard reset, but later models retained F-Lock state across reboots.

Other keyboard manufacturers (such as Logitech and Viewsonic) have also implemented the F-Lock onto their keyboards.