An investment firm is a corporation or trust that invests the aggregate capital of investors in financial securities. Most often, this is done either through a closed-end fund or through an open-ended fund (also called a mutual fund). In the United States, most investment companies are registered and regulated by the Securities and Exchange Commission (SEC) under the Investment Companies Act 1940.
An investment company is also known as a “fund company” or “fund sponsor”. They often partner with third-party distributors to sell mutual funds.