A plate which commemorates a famous person or event and is meant to be hung on the wall as a decoration, rather than being used as a place to put food. I have seen commemorative plates bearing the images of the Virgin Mary, Princess Diana, the election of Bill Clinton, the construction of a new church, the "Dukes of Hazzard" and "Star Trek" TV shows, and of course, Elvis Presley.
If you want a commemorative plate, you usually have to order it out of the back of a magazine or a supermarket tabloid or find one for sale in a second-hand store, 'cause the fine china shops just don't sell 'em. Yeah, they always say they're collectable and will be valuable someday -- they won't.