What is a cyst best defined as?

A cyst is best defined as a swollen area that contains fluid, air, or other material, which can include pus, under the skin. Cysts can occur in various parts of the body and are often encapsulated, meaning they have a distinct wall that separates them from surrounding tissues. They can be filled with semi-solid material, such as keratin, or pure fluid, depending on the type of cyst.

In the context of the other options, a benign raised scar refers to a form of tissue that can develop from the healing process after an injury, which does not align with the definition of a cyst. A crack or fissure in the skin, typically referred to as a skin lesion or tear, is notably different from a cyst structurally and functionally. Lastly, skin erosion describes an area where the outer layer of the skin has broken down or been lost, rather than a distinct swollen area under the skin like a cyst. Thus, the characteristic of housing pus aligns most closely with the definition of a cyst.