A locker was a storage compartment sealed with a door that could be locked. Lockers were generally used to store hand equipment, weapons, or personal items. Lockers were small enough that an average Human could not step into one, and were therefore distinct from storage rooms. A lockers' interior could be subdivided by shelves for more efficient storage.
In 2366, Commander Riker and Lieutenant Commander Data discovered memory coils in an open locker on the Promellian battle cruiser Cleponji. (TNG: "Booby Trap")
Lockers used for storing personal belongings and uniforms were installed in residential hallways of California-class starships in 2380. The decentralization of the lockers and their proximity to crew berths allowed easy access for crew members. (LD: "Second Contact")
In 2381, Ensign Olly hid a damaged vidscreen she discovered in Quadralon's quarters in her locker as part of a ruse to pin Quadralon's disappearance on the Orbs because she feared that, given the electrical damage, her powers would result in her being blamed. After Olly accidentally revealed knowledge of the vidscreen's condition and caused a shape war between the Orbs and Cubes, Lieutenant jg Beckett Mariner tracked it to the locker, kicked it open, and confronted Olly over the ruse. (LD: "Of Gods and Angles")
In 2263 of the alternate reality, Doctor McCoy told Captain Kirk that he had "found" a bottle of Glenfiddich in Pavel Chekov's locker. (Star Trek Beyond)