An organization that is owned by the people it serves. There are many different kinds of cooperative societies, all of which blur the line between "owners" and "customers."
Some of the most common co-operative sociei, there are housing co-ops which are owned collectively by the people who live in its buildings, agricultural co-ops which process and market produce at no profit to itself; credit unions, which function more or less like cooperative banks; and retail co-ops, usually groceries, which sell food to communities.
A co-op functions as a communist organization within a capitalist system. The rules governing co-ops (the cooperative principles provide for a fairly egalitarian, non-profit organization. However, that organization competes in the free market with other corporations. Not all co-ops extend the collaborative model that exists within their organization to the outside world.
Co-ops can be members of the International Cooperative Alliance, which has adopted seven Cooperative Principles that all its members are expected to follow.
Besides credit unions and small groceries, the best-known co-ops in the United States are agricultural marketing co-ops, such as Welch's and SunKist that allow small farmers to market their goods under nationally recognized brand names.