How is a cyst defined?

A cyst is defined as a sac-like structure that can be filled with fluid, pus, or other material that accumulates under the skin. This definition highlights the nature of what a cyst actually is; it is not just a simple bump or lesion but a more complex formation that can vary in content.

Cysts can result from a variety of causes, including infections, blockages of ducts, or physiological processes. By understanding that a cyst is essentially a collection of material that creates a bubble beneath the skin's surface, one can better identify and differentiate it from other types of skin conditions.

The other options describe different skin conditions that do not encompass the full definition of a cyst, such as a raised lesion that specifically contains pus or solid pimples, which are typically different types of inflammatory responses in the skin rather than the encapsulated structure of a cyst.