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. Other generic terms are long-haired house cat and, in British English, long-haired moggie. Domestic long-haired cats are the third most common type of cat in the USA.

In the cat fancy, and among veterinarians and animal control agencies, domestic long-haired cats may be classified with organisation-specific terminology (often capitalized), such as Domestic Longhair (DLH), House Cat, Longhair (HCL), or Semi-Longhair Household Pet. Such a pseudo-breed is used for registry and shelter/rescue classification purposes, and breeds such as the Persian cat. While not bred as show cats, some mixed-breed cats are actually pedigreed and entered into cat shows that have non-purebred "Household Pet" divisions. Show rules vary; Fédération Internationale Féline (FIFe) permits "any eye colour, all coat colours and patterns, any coat length or texture, and any length of tail" (basically any healthy cat). Others may be more restrictive; an example from the World Cat Federation: "The colours chocolate and cinnamon, as well as their dilution (lilac and fawn) are not recognized in any combinations...[and] the pointed pattern is also not recognized".

Domestic long-haireds come in all genetically possible cat colours including tabby, tortoiseshell, bi-coloured, and smoke. Domestic long-haireds can have fur that is up to six inches long. They can also have a mane similar to a Maine Coon's, as well as toe tufts and ear tufts. Some long-haired cats are not able to maintain their own coat, which must be frequently groomed by a human or may be prone to matting. Because of their wide gene pool, domestic long-haireds are not predisposed to any genetically inherited problems.