Tendonitis (or Tendinitis) - An inflammation (swelling) of the tendon.
 
Tendon - Fibrous tissue, that connects muscle to bone.
 
Tennis Elbow - It has earned this name because of the common occurrence in tennis players (constant dorsiflexion of the wrist.) Where in fact, it is an Inflammation at the lateral epicondyle (bony process of the humerus) of the elbow and the tendons insertions, and can happen to many.