This is an inflammation of a tendon at the back of your elbow. It's called the "triceps" tendon. It anchors your upper arm's triceps muscle to the ulna (one of the bones of your forearm).
You can injure your triceps tendon by repeatedly stressing it. Baseball pitchers are prone to this injury. It can also be a problem for weightlifters. You may be at risk if your job requires you to do a lot of hammering or other stressful motions that involve your elbow.
Triceps tendonitis causes pain in your elbow. You may feel the pain with activity but not when your arm is at rest. Eventually, your elbow may hurt all the time. The tip of your elbow may feel tender. Your elbow may be swollen, and it may be hard for you to straighten your arm.
Treatment options may include rest, ice, compression and elevation. You may benefit from medication and physical therapy. Other options may also help. If these aren't helpful, you may need surgery. Your healthcare provider can create a plan that's right for you.