Anything a pet can wear for the purposes of protection, decoration, or control (e.g. clothing or costumes).
Attire questions regard clothing a pet may wear, but can also extend to costuming, and other controlling or protective items which can be worn by a pet (for example, sweaters or a comfort device such as a harness, shirt, or vest). Boots and socks; anything that an animal could wear, is covered by attire.
Questions of attire may include how to create, how to measure, how to get a pet to wear, how to remove, habit concerns (such as a pet that enjoys wearing certain items), and proper application (appropriate Thundershirt usage, for example).