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 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)