Mad Dog: A rabid dog.

Mahogany: Used to describe several breeds, this color is a medium-saturated, dull, reddish brown. Color definitions may vary by breed. Always check the breed standard for the definitive color description.

Marking: An instinctual behavior in which male dogs urinate in certain locations to establish their territory.

Making a Wheel: Term given to the circling of the tail over the back.

Mandible: The bone of the lower jaw.

Mane: Long, thick hair on top and sides of neck.

Mantle: Dark-shaded portion of the coat on shoulders, back, and sides.

Manubrium: The first sternabra of the chest.

Marcel Effect: Regular continuous waves (specified in the American Water Spaniel standard).

Markings: Contrasting color or pattern in a dog's coat.

Mask: Dark shading on the foreface.

Mastiff: An ancient breed of large strong dogs, probably originating in Asia and having a short, often fawn-colored coat.

Mastitis: Inflammation of the breast or udder.

Mate: To breed a dog and bitch.

Maternal Immunity: A form of temporary immunity passed from a mother to her offspring while in the uterus and after birth in the colostrum and milk.