What is the term for a localized collection of pus?

The term for a localized collection of pus is "pustule." This is defined as a small inflamed elevation of the skin that is filled with pus, often a result of infection or inflammation. Pustules are commonly associated with conditions like acne, folliculitis, and various skin infections, where the accumulation of pus indicates the body's immune response to a pathogen.

The other terms listed describe different medical conditions that are not synonymous with a localized collection of pus. A vesicle refers to a small fluid-filled sac that can arise from conditions like blistering. A granuloma is a type of inflammation characterized by the formation of a mass of tissue due to chronic inflammation, often associated with conditions like tuberculosis or sarcoidosis, but it is not primarily a pus-filled area. Phlegmon is a diffuse inflammatory process that affects connective tissue and often involves pus, but it does not refer to a localized collection as specifically as a pustule does.