You might use a locker at school, when you're visiting a museum and need a place to leave your backpack, or at the gym. In fact, most gyms and swimming pools have "locker rooms," where you can change into your workout clothes and store your regular clothes and shoes, as well as your wallet, phone, and keys, in a locker. Locker has been used since the 14th century — and even earlier, although it originally meant "a lock."