You may be describing the anterior drawer test. This is a test for ligament laxity or looseness. The lower leg bone (tibia) slides or glides forward underneath the thighbone (femur). A certain amount of slide or glide is normal. Too much sliding around is a sign that one of the ligaments inside the knee joint may be torn or damaged.
There is a series of tests for knee ligaments. If you've had the anterior drawer test, you've probably also been tested for side-to-side and rotational motion. All of these movements are needed for normal motion. Too much or not enough joint "play" or laxity can cause problems and put you at risk for future injury.