Investors can be generally categorized into three groups: retail investors, semi-professional investors, and professional investors.
In this classification, institutional investors belong to the category of professional investors. Almost all institutional investors are considered professional, although not all professional investors are institutional.
In common language, there is often no distinction made between institutional and professional investors. However, there are cases in which a wealthy private investor, due to the scale of their financial and market activities, may be classified as a professional investor to access certain opportunities or to bypass regulatory requirements that apply to retail investors.
In contrast, institutional investors, by definition, are not private individuals but rather legal entities that operate in the market.