What is it called when combination of firms or corporations formed by a legal agreement?

A combination of firms or corporations formed by a legal agreement is commonly referred to as a "conglomerate" or "joint venture." These arrangements allow companies to collaborate for mutual benefit, often sharing resources, expertise, or capital to pursue specific business objectives. In some cases, such combinations may also be structured as mergers or acquisitions, depending on the nature of the agreement and the level of integration between the entities.