If this is referring to the windows driver type called a "keyboard filter driver" is a driver that sits in the keyboard data chain and can "spy" on your keystrokes before or after the windows driver handles the data.

Card readers frequently use the keyboard filter when attached to keyboards in order to trap the characters coming off the card reader and redirect them to a special program rather than have the card data show up in a random edit field in windows.

It enables you to configure key combinations that you want to prevent users from entering from a keyboard.

Keyboard filters

external image 62614-2.jpg
external image 29F0818-1SR-10.jpg
external image ikey.jpg