1. A coat typically extending only from the shoulders to the waist or slightly below it: Everyone should have a light jacket for the cool days of spring.
2. A covering for the outside of a book designed to protect it: The book was protected by a jacket of clear plastic.

A paper cover which protects a book and that can be easily removed: The dust jacket of one of the used books was torn; however, the other books had dust jackets that were still in very good condition.