A 
supermarket is a large shop for groceries and other goods, including meat and fresh produce. It's a full service grocery store that often sells a variety of non-food products as well. Almost always part of a chain; e.g. Tesco, Safeway. Stores that do not provide full service grocery departments, including meat and fresh produce, are generally not considered supermarkets for historical reasons.
How to map
Set a node or draw as an area along the shop outline. Tag it with shop=supermarket and name=*.
Tags used in combination
Similar tags
shop=convenience- Typically much smaller than a supermarket, and typically carries a more limited selection of food items. One suggestion for distinguishing between a supermarket and a convenience shop, is that a supermarket is large enough to use trolleys.shop=variety_store- A price-point retailer selling inexpensive items. These can have aisles and trolleys but normally little or no fresh food or produce.shop=general- A general store. Selling various things. This tag is a little unclear for various reasons, but a supermarket has more of an emphasis on food.shop=department_store(and Proposed features/department store) - a large store with multiple clothing and other general merchandise departments. These are less likely to have shopping trolleys and smooth floors for wheeling them. They have little or no area given over to food items. A department store that sells a full selection of groceries (e.g. Walmart Supercentre) which is often called a "hypermarket" should be taggedshop=supermarketshop=wholesale- A large store which sells items in bulk.
Related features
amenity=trolley_baySome supermarkets may include also separate shops and objects, separate from the main supermarket shop. It is OK to map them independently: