A big-box store (also supercenter, superstore, or megastore) is a physically large retail establishment, usually part of a chain of stores. 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 general merchandise retailer (however traditional department stores, as the predecessor format, are generally not classified as "big box"), 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, whereas in the U.S. there is no specific term for the format, which both Target and Walmart offer in most branches.
Typical architectural characteristics include the following:

Large, free-standing, cuboid, generally single-floor structure built on a concrete slab. The flat roof and ceiling trusses are generally made of steel, and the walls are concrete block clad in metal or masonry siding.
The structure typically sits in the middle of a large, paved parking lot. It is meant to be accessed by vehicle, rather than by pedestrians.
Floor space several times greater than traditional retailers in the sector, providing for a large amount of merchandise; in North America, generally more than 50,000 square feet (4650 m2), sometimes approaching 200,000 square feet (18,600 m2), though varying by sector and market. In countries where rentable space is at a premium, such as the United Kingdom, the relevant numbers are smaller and stores are more likely to have two or more floors.Big box stores are often clustered in shopping centers known as retail parks in the U.K. and, in the United States, when they range in size from 250,000 square feet (23,000 m2) to 600,000 square feet (56,000 m2), they are referred to as power centers.Commercially, big-box stores can be broken down into two categories: general merchandise (examples include Walmart, Kmart and Target), and specialty stores (such as Home Depot, Barnes & Noble, or Best Buy) which specialize in goods within a specific range, such as hardware, books, or consumer electronics respectively. In the late 20th and early 21st centuries, many traditional retailers—such as Tesco and Praktiker opened stores in the big-box-store format in an effort to compete with big-box chains, which are expanding internationally as their home markets reach maturity.