As used in this article the term “joint venture” means a separate employing unit which has been organized by two or more employers to accomplish a contract or project or series of contracts or projects and which is wholly owned by such employers. As used in this section only, “employer” means any individual or type of organization, including any partnership, joint venture, association, trust, estate, joint stock company, insurance company, corporation whether domestic or foreign, and the receiver, trustee in bankruptcy, trustee or successor thereof, and the legal representative of a deceased person.