The term "vanity" is used within World of Warcraft to refer to items or elements that have no combat or gameplay significance, but rather are desired for cosmetic effects or just as fun items. This includes gear that looks good but has bad stats, disguises, and items that have entertaining effects. "Vanity pet" is another name for a companion or non-combat pet.
On RP servers vanity items are sometimes called props.
Multiple items that have been designed to work well together for vanity purposes are called a vanity set.