What is described as an encased collection of pus?

An encased collection of pus is referred to as an abscess. An abscess forms when a localized infection leads to the accumulation of pus in a tissue, organ, or confined space within the body. This pus typically contains dead white blood cells, bacteria, and tissue debris, which are products of the body's inflammatory response to infection. The body often encapsulates an abscess with a fibrous wall to prevent the spread of infection, leading to its encapsulated nature.

In contrast, a cyst is a closed sac-like structure that can be filled with fluid, air, or other material but does not necessarily contain pus. A fistula is an abnormal connection between two body parts, usually resulting from disease or injury and not defined by pus collection. A sarcoma is a type of cancer that arises from connective tissues, such as bone, muscle, and cartilage, and is unrelated to the concept of a pus-filled cavity. Understanding these distinctions highlights why an abscess is specifically characterized as an encased collection of pus.