Mini Bar  is a specially designed small floor mounted refrigerator located in guest rooms containing a variety of snacks and drinks, with individual guest Room key access. This amenity serves as a more profitable substitute for room service.
Other definition:
Mini bar is the small refrigerator and/or counter space in hotel rooms stocked with drinks and refreshments for guest use. Often with key access, principally if alcoholic drinks are provided. Items are usually much costlier than if purchased in local shops.