As an adjective, cooperative describes working together agreeably for a common purpose or goal as in cooperative play or cooperative employee.
As a noun, a cooperative is a jointly-owned business or enterprise where members pool their resources to purchase, do work, and/or distribute things. You might join a food cooperative, for example, which jointly purchases a farmer's labor and then every member gets a basket of fresh fruits and vegetables each week of the growing season. In this use, the word is often shortened to co-op. You might also join a housing cooperative where you own your apartment and you and the other owners jointly care for the upkeep of the building and grounds.