What is the term for a birthmark or mole?

The term for a birthmark or mole is "nevi." In dermatology, nevi refers to benign, pigmented lesions that are commonly known as moles. These growths are typically formed from clusters of melanocytes, the cells responsible for producing melanin, which gives skin its color.

Nevi can vary in appearance, ranging from flat and small to raised and larger, but they are generally harmless unless there are changes in size, shape, or color, which could indicate potential issues such as skin cancer. Understanding this term is essential for recognizing common skin conditions and communicating effectively about skin health.

The other terms provided do not relate to skin lesions: "bulb" can refer to a plant structure or the base of a hair follicle, "photon" is a particle of light relevant in physics, and "neutron" is a subatomic particle found in the nucleus of an atom. Thus, "nevi" is the appropriate term when referring to birthmarks or moles in the context of skin.