A cover model is a male or female whose photograph appears on the front cover of a magazine or book. The cover model is generally a fashion model, celebrity or contest-winner. Generally cover models are depicted solitary, however on occasion will be presented on a front cover with multiple cover models.
Cover Models are more well known among photographers and graphic designers. However, some models looking to get into book cover models will pass out cards at author conventions. Authors, normally, have the final say on what is present on the cover of their books so models approaching authors is not to uncommon.
When talking to a cover model make sure you tell them exactly what you are visioning for your cover to look like. The emotion on the face, the direction their body faces, the way they turn their head. Also now with the age of Photoshop just because a model has green eyes and you need blue don't turn them down because a good graphic designer can change the eye color for you. I've met a few Cover Models and they are always really nice to talk to and fun to joke around with.