Domestic Long Hair is a coat description, not a breed. It covers mixed-ancestry cats with medium to long fur, in every color and pattern, and some resemble a Maine Coon or Persian without sharing that lineage. Because no standard shapes them, size and looks vary a lot, and most adults land between 8 and 15 pounds.
What they have in common is upkeep. Longer fur tangles behind the legs, under the belly and around the tail, so brushing a few times a week keeps mats and hairballs down. Personality is just as varied. Some cats are lap-sitters and others are shy or independent at first, so spend time with the cat in front of you rather than counting on the label.