What term describes a local collection of pus?

The term that describes a local collection of pus is "abscess." An abscess forms when an infection occurs in a tissue, leading to the accumulation of pus, which is composed of dead white blood cells, bacteria, and tissue debris. This condition often results in swelling, redness, pain, and can sometimes cause fever as the body ramps up its immune response to fight off the infection.

In contrast, an ulcer refers to a sore or lesion on the skin or mucous membranes that may lead to a decay of tissue but is not specifically a collection of pus. A scar results from the healing of a wound, which can occur after an abscess has formed and been drained. A blister is a fluid-filled sac that typically forms due to friction, burns, or certain medical conditions and does not pertain to pus accumulation.

Thus, "abscess" accurately captures the definition of a localized pocket of infection and pus, making it the correct choice.