Tennis elbow is a common injury and got its' name because tennis players tend to get it. It could equally well be called "plasterer's elbow" or "mechanic's elbow" or "painter's elbow".
The medical name for tennis elbow is lateral epicondylitis of the humerus. Lateral means "on the side" and refers to the area of the elbow away from the body. The humerus is the largest bone in the upper arm and has rounded bony protrusions on both sides of the elbow that are called epicondyles. The muscles that extend or straighten the wrist and fingers derive origin in part from the lateral epicondyle. Tennis elbow refers to a degenerative or traumatic tear of these tendon origins at their attachment to the bone, causing pain on the outside of the elbow. The majority of people getting this are between 40 and 50 yrs but it can affect any age.