Definition. Company that actively manages an investor's assets and/or equity in order to achieve the investor's financial objectives. These companies are available to both private and institutional investors. Some may use aggressive growth strategies, while others may invest in passive index funds.ompany that actively manages an investor's assets and/or equity in order to achieve the investor's financial objectives. These companies are available to both private and institutional investors. Some may use aggressive growth strategies, while others may invest in passive index funds.