pustule

This term describes a specific type of skin lesion characterized by the presence of purulent exudate. It is primarily used in medical and clinical contexts to distinguish a pus-filled blister from a vesicle, which contains only clear fluid, or a papule, which is a solid bump. Because it refers to a discrete physical lesion, it is treated as a standard countable noun. In clinical reports, it is often used to describe the morphology of an eruption, such as in the case of acne or varicella.