A Passion Project used to be a term reserved for kids at school. The new digital economy is making it relevant to adults. It's a project you're passionate about that you can pursue without quitting your job or education. Examples include learning to play the guitar, writing a book or developing a new digital service. Your passion project may even be the launch pad of the next big company that will help make the world a better place.
https://www.ted.com/talks/steven_johnson_how_play_leads_to_great_inventions/transcript?language=en