A SLAP tear is an injury to a piece of shoulder cartilage called the labrum. This cartilage surrounds the shoulder socket, helping to keep it stable when you move. Your arm muscle (biceps) is attached to your shoulder by a biceps tendon. This tendon connects your biceps to the labrum at the top of the shoulder joint. A SLAP tear happens when the labrum is damaged where the biceps tendon is attached.
This picture shows one type of SLAP tear. SLAP stands for Superior Labrum Anterior to Posterior.