By Annette Badowski Tennis elbow (or lateral epicondylitis) is an inflammation of the tendon that attaches to the bony, somewhat knobby, outermost portion of the elbow. The term tennis elbow is something of a misnomer however, as only a small population of tennis players get the condition in comparison to everyone else. Tennis elbow is most commonly found in people between 35 and 55 years of age.