Domestic Medium Hair is a coat description, not a breed. It's the label used for mixed-ancestry cats whose fur falls between short and long: fluffier than a domestic shorthair, often with a plumed tail, tufts between the toes and a soft undercoat, but without a longhair's heavy ruff. They come from the general cat population, so every color and pattern turns up, from tabby and tuxedo to calico and solid black.
Because ancestry is mixed, size, personality and health vary from cat to cat. Most adults weigh 6 to 14 pounds and live 12 to 18 years. In State College, plan on a bit more brushing than a shorthair needs, especially in spring and fall when the undercoat lets go. Meeting the cat is the best guide to temperament.