portfolio company
Investment firms, like venture capital firms, refer to the companies in which they have invested as "portfolio companies." This is because the investment firm will typically invest in 10-30 companies per fund. So a typical investment firm will manage a large array of investments. Because the investment firm receives equity in each company in which it invests money, it is a part owner of a large group of companies. It calls these companies "portfolio companies" and will often refer to its basket of investments as its "portfolio" borrowing simliar terminology from public stock investors like mutual funds.