The term melanism refers to black pigment and is derived from the Greek: μελανός. Melanism is the increased development of the dark-colored pigment melanin in the skin or hair.

Melanism is the opposite of albinism, and leucism, conditions that can turn animals white.

Pseudomelanism, also called abundism, is another variant of pigmentation, identifiable by dark spots or enlarged stripes, which cover a large part of the body of the animal, making it appear melanistic.

The morbid deposition of black matter, often of a malignant character causing pigmented tumors, is called melanosis.

More Info: en.wikipedia.org