Definition from Innovation Leader
“An individual investor who offers funding, mentoring, introductions, and other help with the eventual goal of a return on investment. Angels usually invest at the earliest, or seed stage, before venture capitalists get involved with a company.”
Going further
I've curated 400+ definitions just like this one in a tiny dictionary. In this glossary you can easily access, search and understand 400+ terms that service designers and other innovators use.