**Core Concept**
Quinsy, also known as a peritonsillar abscess, is a collection of pus behind the tonsils that can be a complication of tonsillitis. This occurs due to the spread of infection from the tonsils to the tissues surrounding them.

**Why the Correct Answer is Right**
In quinsy, the collection of pus is found in the peritonsillar space, which is the area between the tonsil and the superior constrictor muscle of the pharynx. This space is located anterior to the tonsillar fossa and can become infected, leading to the formation of an abscess. The peritonsillar space is a potential space that can accumulate pus due to the spread of infection from the tonsils.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the location of quinsy.
* **Option B:** This option is incorrect because the submandibular space is not directly related to the formation of quinsy.
* **Option D:** This option is incorrect because the parapharyngeal space is a different location that can also be involved in infections, but it is not the primary location for quinsy.

**Clinical Pearl / High-Yield Fact**
Quinsy is a serious complication of tonsillitis that requires prompt medical attention to prevent further complications, such as airway obstruction or abscess rupture.

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