Calico is a coat pattern rather than a breed: white with patches of black and orange, or soft gray and cream in the dilute version. The pattern appears in domestic shorthairs, longhairs and many pedigreed cats, and nearly all calicos are female because the color genes sit on the X chromosome.
Most calicos waiting for adoption are domestic shorthairs, so expect an ordinary house cat's size, coat and health, typically 6 to 12 pounds and 12 to 18 years. Coat color doesn't predict personality, so the cat's age, history and behavior with people tell you far more. Shedding is moderate, which means regular brushing, and a longhaired mix needs it more often.