Like the domestic short-haired cat, this is not a breed, but a non-breed classification of mixed-breed cats.
Domestic cat (Felis catus)
A domestic long-haired cat is a cat of mixed ancestry – thus not belonging to any particular recognised cat breed – possessing a coat of semi-long to long fur. Domestic long-haired cats should not be confused with the British Longhair, American Longhair, or other breeds with "Longhair" names, which are standardized breeds defined by various registries. Domestic long-haireds are the second most popular cat in the United States after the domestic short-haired; one in ten of the ninety million cats in the US is a domestic long-hair. Other generic terms are long-haired house cat and, in British English, long-haired moggie. Source: https://en.wikipedia.org/