When you think of holes, what comes to mind? Maybe the irritating hole in your sock. Or the hole on the shelf where you plucked out this book. But did you know there are holes that suddenly devour entire gas stations? Big holes in the ocean that are visible from space? Small holes in balls that prevent a backyard home run? A hole is a part of something where there's nothing at all. Holes are investigated by scientists, used by artists, designed by engineers, and fixed by problem-solvers. They can be natural or human-made, big or small, plentiful or scarce, mysterious or painfully familiar. Many are important to our everyday lives, whether we give them credit or not. Back matter explores language and vocabulary.