What is another term for a birthmark, caused by abnormal pigmentation or dilated capillaries?

A birthmark is commonly referred to as a nevus. This term specifically describes a variety of pigmented lesions that can appear on the skin, some of which are present at birth. Nevi can result from an overgrowth of melanin-producing cells or a cluster of blood vessels, which can give rise to the abnormal pigmentation or the characteristic appearance of dilated capillaries. This makes "nevus" the appropriate term to describe these types of skin marks.

The other terms mentioned have distinct meanings in dermatology. A nodule refers to a solid, raised bump on the skin that is greater than 1 centimeter; a macule denotes a flat, discolored area on the skin that is less than 1 centimeter; and milia are small, white cysts that typically occur in newborns or as a result of skin damage in adults. These terms do not refer to the same type of skin condition as a birthmark or nevus.