This is a huge Tibetan mastiff

The name Tibetan mastiff is a misnomer, as the breed is not a true mastiff. The term mastiff was assigned by the Europeans who first came to Tibet because that name was used to refer to nearly all large dog breeds in the West. Early Western visitors to Tibet misnamed several of its breeds, such as the Tibetan terrier, which is not a terrier, and the Tibetan spaniel, which is not a spaniel. A better name for the breed might be the Tibetan mountain dog or—to encompass the landrace breed throughout its range—the Himalayan mountain dog