Angel investor:

An angel investor or "angel" (also known as a business informal investor) is an affluent individual or company who provides funds for a business start-up, usually in exchange for ownership equity or convertible debt. An Accredited Angel Investor is having met criteria as defined by the SEC required to invest in a business or project. An increasing number of angel investors organize themselves into companies, angel groups or angel networks to share research and pool their investment capital. Sophisticated angel investors are known as "super angels" and may be a single investor for entire business or project.