Bookends are objects placed at each end of a row of books to hold them upright on a shelf. Usually made of wood, metal, or another heavy material, bookends work like sturdy barriers that keep your books from toppling over like dominoes. Without them, books would slump sideways into messy piles.

The word also describes things that mark the beginning and end of something else. Two storms might bookend a sunny week. A teacher might bookend a lesson by starting and finishing with the same story. In movies, directors sometimes bookend their films with similar scenes at the start and finish, creating a satisfying sense of completion.

When you hear that two events bookend a period of time, picture them like actual bookends: one stands at the beginning, one at the end, and everything else fits between them. A family vacation might be bookended by two long car rides, or your school year might be bookended by the first day of class in September and the last day in June.