Tennis elbow is a painful condition affecting the outside part of the elbow. This area is called the lateral epicondyle and so the medical term for this condition is lateral epicondylitis. Tennis elbow is usually caused by overuse of the forearm. Many forearm muscles attach at or around the lateral epicondyle so when they are overused they pull too much on the elbow and make it sore. Common problematic activities include tennis (especially backhands), using a screwdriver, drilling and repeated keyboard and mouse use.
Pain and tenderness is usually felt on the outside of your dominant elbow and into the upper forearm. The pain is often aggravated by wrist movements, gripping and anything which requires use of forearm muscles.
Resting the elbow, icing it after activity, wearing a high quality lateral eipicondylitis clasp (see below) and regularly stretching your forearm muscles can all help reduce your symptoms.