An irritation of the tissue connecting the forearm muscle to the elbow. Tennis elbow, or lateral epicondylitis, is a condition in which the forearm muscles become damaged from overuse. Tennis elbow is a pain focused on the outside of your arm, where your forearm meets your elbow. Tennis elbow is a type of tendinitis -- swelling of the tendons -- that causes pain in the elbow and arm. Tennis elbow (lateral epicondylitis) is a painful condition that occurs when tendons in your elbow are overloaded, usually by repetitive motions. Tennis elbow, or lateral epicondylitis, is a painful inflammation of the elbow joint caused by repetitive stress (overuse).