Final answer:
The posterior faucial pillar is known as the palatopharyngeal arch, a muscular fold that contributes to the action of swallowing and houses the palatine tonsils, which are part of the body's immune system.
Step-by-step explanation:
The posterior faucial pillar is also called the palatopharyngeal arch. This muscular fold extends from the lateral side of the soft palate to the side of the pharynx. The palatopharyngeal arch forms the superior and lateral margins of the fauces. Between the palatopharyngeal arch and the palatoglossal arch, which lies toward the front, are the palatine tonsils, clusters of lymphoid tissue that protect the pharynx. When you swallow, the soft palate and uvula move upward, aiding in the prevention of foods and liquids entering the nasal cavity, and the palatopharyngeal arch plays a role in this mechanism.