Wiktionary
n. 1 a large retail store holding a wide selection of goods for sale at discounted prices to members of the club 2 the club itself
Wikipedia
A warehouse club is a retail store, usually selling a wide variety of merchandise, in which customers may buy large, wholesale quantities of the store's products, which makes these clubs attractive to both bargain hunters and small business owners. The clubs are able to keep prices low due to the no-frills format of the stores. In addition, customers may be required to pay annual membership fees in order to shop.
The concept is similar to the consumers' cooperative supermarkets found in Europe, though using bigger stores and not co-operatively owned. The use of members' prices without co-operative ownership is also sometimes used in bars and casinos.