What term is used to describe sole proprietorships, partnerships, and corporations as private producing units in the economy?

The term that is commonly used to describe sole proprietorships, partnerships, and corporations as private producing units in the economy is "firms." Firms are the entities that engage in the production of goods and services and make up the business sector of the economy. In economics, firms are recognized for their role in organizing inputs and utilizing resources to create products that can be sold in markets.

While "businesses" might seem like it fits well, it is a broader term that encompasses any economic activity designed to produce goods or services. "Enterprises" often has a more entrepreneurial connotation, usually referring to more substantial commercial ventures. "Institutions" typically denotes established laws, practices, or norms that govern behavior in the economy, rather than units of production. Therefore, the specific use of "firms" captures the essence of the entities engaged in production accurately within the context of economic discussions.