is the generic term for different types of skin anomalies that develop from melanocytes, melanin-containing cells that give the skin its color. Among the various types of nevi, the most frequent are simple or common pigmented nevi, which are for the most part what a layperson would call a mole or birthmark. A mole is typically a patch of skin that is more pigmented than the surrounding skin, flat or slightly elevated, that usually stays the same or changes only slightly through the course of a lifetime. Other types of nevi can be of different colors, from all the possible tones of brown to blue. The greatest risk with certain nevi is the possibility they will evolve into a malignant tumor, namely a melanoma
, which is cancerous and requires immediate surgical removal.