Willynanita, I wish I knew what it’s called but there is a cantilevered device on springs and brackets. You would mount the brackets to the bottom side of your desk and place your keyboard on the shelf tucked away below your desktop. When you need the keyboard, you simply pull the shelf out from the bottom of the desk and it would become level with the top sides of the desk with the depth of your keyboard and it’s’ shelf will be extended in front of you.
Once it is no longer needed, you release the catch and press the shelf (with keyboard) back under the desk. Try kitchen cabinet places or online catalogs…my mom had this for her kitchen aid mixer which she could never lift…this made it perfect for her to pull up and out and the tuck away.