The difference between a joint venture and a business is that a business is one company, one firm, and a joint venture is a project in which two or more companies join together. So a joint venture involves more than one firm or business.
A joint venture occurs when one or more different firms get together and work together on one particular project. The firms do not merge, they just cooperate. They remain as separate entities, but they work together on this one project. After the project is over, they do not necessarily work together again. Joint ventures are typically undertaken so as to share risks or so as to allow a company from one country to gain entry into another country's market.
So the difference between the two is that a business is one company while a joint venture is when more two or more companies cooperate on a project.