A big-box store (also supercenter, superstore, or megastore) is a physically large retail establishment, usually part of a chain. The term sometimes also refers, by extension, to the company that operates the store. The store may sell general dry goods in which case it is a department store, or may be limited to a particular specialty (such establishments are often called "category killers") or may also sell groceries, in which case some countries (mostly in Europe) use the term hypermarket.

A category killer is a product, service, brand, or company that has such a distinct sustainable competitive advantage that competing firms find it almost impossible to operate profitably in that industry (or in the same local area). The existence of a category killer eliminates almost all market entities, whether real or virtual. Many existing firms leave the industry, thereby increasing the industry's concentration ratio.