**Core Concept**
Tennis elbow, also known as lateral epicondylitis, is a condition characterized by inflammation of the extensor tendons of the forearm, leading to pain and tenderness on the lateral aspect of the elbow. This condition is commonly seen in individuals who engage in repetitive activities that involve gripping or twisting motions, such as tennis, golf, or using tools.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of tennis elbow, which involves micro-tears in the extensor tendons of the forearm. The extensor carpi radialis brevis (ECRB) muscle is particularly affected, as it is responsible for wrist extension and radial deviation. The repetitive strain on this muscle tendon leads to inflammation and pain, which is exacerbated by activities that involve gripping or twisting motions.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because tennis elbow is not primarily characterized by medial epicondylitis, which is a different condition known as golfer's elbow.
* **Option B:** This option is incorrect because tennis elbow is not primarily characterized by inflammation of the biceps tendon, which is a different condition.
* **Option C:** This option is incorrect because tennis elbow is not primarily characterized by inflammation of the flexor tendons of the forearm.

**Clinical Pearl / High-Yield Fact**
A key clinical feature of tennis elbow is pain on extension of the wrist against resistance, which can be elicited by the examiner.

**Correct Answer: C. Inflammation of the extensor tendons of the forearm.**