**Core Concept**
Tuberculosis (TB) of the skin is a form of extrapulmonary tuberculosis, which occurs when Mycobacterium tuberculosis infects tissues outside the lungs. This condition can manifest as a localized skin lesion or as a systemic infection.

**Why the Correct Answer is Right**
TB of the skin is often referred to as **cutaneous tuberculosis**. This is because the bacteria infect the skin, leading to inflammation and tissue damage. Cutaneous TB can be primary or secondary, with the latter often resulting from reactivation of latent TB infection. The bacteria can enter the skin through cuts, abrasions, or other breaches in the skin barrier, or through hematogenous spread from an internal site of infection.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not a recognized term for TB of the skin.
**Option B:** This option is incorrect because it is a type of skin lesion, but not a specific term for TB of the skin.
**Option C:** This option is incorrect because it is a different type of skin condition altogether.

**Clinical Pearl / High-Yield Fact**
Cutaneous TB can be challenging to diagnose, as it may resemble other skin conditions. A high index of suspicion and careful clinical evaluation, including microscopy and culture of skin lesions, are essential for accurate diagnosis.

**Correct Answer: C. Lupus vulgaris. Lupus vulgaris is the most common form of cutaneous tuberculosis.**