An oversized king mattress is a bed larger than a standard king or California king. Examples include Wyoming king, Alaskan king, and Texas king mattresses:
A Wyoming king is 84 inches by 84 inches.
An Alaskan king is 108 inches by 108 inches.
A Texas king is 80 inches by 98 inches.
Because these beds are nonstandard sizes, they usually have to be custom ordered from an online mattress manufacturer.