Final answer:
An epidermal cyst is a common, non-cancerous lesion on the epidermis, often filled with keratin or fluid, which can be raised, discolored, and sometimes pus-producing.
Step-by-step explanation:
An epidermal cyst is typically described as a small, raised bump on the skin, which may sometimes produce pus (suppurative) and contain fluid or keratin. These cysts are benign and usually occur within the epidermis, the outermost layer of the skin that contains dead, keratinized cells. They are derived from the structures associated with hair follicles, particularly the external root sheath. Cysts can arise in any organ but are most commonly found in subcutaneous tissue. They may vary in appearance, some presenting as smooth spots of discoloration while others exhibit less defined boundaries. However, a characteristic feature of an epidermal cyst is its round shape, which is filled with a thick, yellow substance that is mostly composed of dead skin cells.