From Wikipedia: The typical caper story involves one or more crimes (especially thefts, swindles, or occasionally kidnappings) perpetrated by the main characters in full view of the reader. The actions of police or detectives attempting to prevent or solve the crimes may also be chronicled, but are not the main focus of the story. The caper story is distinguished from the straight crime story by elements of humor, adventure, or unusual cleverness or audacity.
From Crimespace: that a heist novel is more noirish and gives you the feeling that everything will inevitably go to hell in a handbasket but a caper novel is a little more upbeat and there’s a feeling that the participants might actually pull it off.
Hmm … think I just figured out that last little detail for my WIP, Mine By Design, to tip me over into a crime caper. Thanks for the clarification, Internet!