Naevus is a medical term that refers to a skin lesion that appears flat, raised, or discolored. Synonyms for naevus include mole, birthmark, blemish, lesion, spot, growth, and nevus. While many naevi are harmless, some can be a sign of skin cancer, so it's important to keep an eye on any changes in size, color, or shape. Melanocytic naevus is a common type of mole, while a birthmark is a type of skin lesion that appears at birth or shortly after. Other types of naevi include acne keloidalis, blue naevus, spider naevus, and halo naevus. Consulting a dermatologist is recommended if one is unsure about a skin lesion.