What is a small collection of pus on the top layer of skin or beneath called?

A small collection of pus that forms on the top layer of skin or beneath it is referred to as a pustule. Pustules are characterized by their raised, inflamed appearance and contain pus, which is a thick fluid composed of dead white blood cells, bacteria, and tissue debris. This type of skin lesion is commonly associated with infections, acne, or inflammatory conditions.

In contrast, options such as a vesicular lesion would refer to a fluid-filled sac, often associated with conditions like chickenpox or herpes, and does not contain pus. The term "fungal" pertains to infections caused by fungi, which would not specifically describe a pus-filled lesion. An abscess, while also a collection of pus, typically refers to a deeper collection that is encapsulated within tissue, rather than being a surface-level pustule. Thus, the term "pustular" accurately captures the characteristics of the described skin condition.