This what is usually ment when someone refers to a mastiff. Old English mastiffs are descended from the Tibetan mastiff, which were introduced to Europe by the Phoenicians. In Great Britain they were breed to be a bloodthirsty fighting dogs, to be used as guard dogs.
They have since been un-breed, and now are gentle dogs that make affectionate pets. Mastiffs are heavy, big dogs; minimum height is 30 in. for males, 27 1/2 for females. Weight 79-86 kg. (175-190 pounds). They have wide heavy heads, with slightly pendent lips.
Mastiffs look somewhat like a heavy Rottweilers, and Rottweiler are probably descended from Italian mastiffs.