**Core Concept**
Peritonsillar abscess is a collection of pus that forms between the tonsillar area and the superior constrictor muscle, typically due to a complication of tonsillitis. This condition is characterized by severe pain, difficulty swallowing, and a tender mass in the throat.

**Why the Correct Answer is Right**
A peritonsillar abscess occurs when an acute tonsillitis progresses to a purulent collection of fluid that forms between the tonsil and the superior constrictor muscle. This is often due to an obstruction of the lymphatic drainage from the tonsil, leading to the accumulation of pus. The superior constrictor muscle is a key anatomical structure in this condition, as it forms the border of the tonsillar fossa and separates the peritonsillar space from the pharynx.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a submandibular lymph node enlargement would typically be located below the mandible, not between the tonsillar area and the superior constrictor muscle.
**Option B:** This option is incorrect because a parapharyngeal abscess would typically be located more posteriorly, in the parapharyngeal space, rather than between the tonsillar area and the superior constrictor muscle.
**Option C:** This option is incorrect because a retropharyngeal abscess would typically be located in the retropharyngeal space, which is more posterior and superior to the tonsillar area.

**Clinical Pearl / High-Yield Fact**
The key clinical feature of peritonsillar abscess is severe pain, which is often out of proportion to the physical findings. This condition requires prompt medical attention to prevent complications such as airway obstruction or sepsis.

**Correct Answer:** C. Peritonsillar abscess.