"booksends" used in figurative speech is a bit more specific than Steffen suggests, as it really refers to the beginning and end of a thing: "...referring to two people or two incidents or ideas that are much the same and can or do support or surround something." The first reference gives sample sentences, and the second provides a more detailed, elaborate explanation in the context of using "bookends" as a speech technique. It's also used in advertising and film as a framing mechanism.