To me "Start-up" always indicated a business (which not all projects are; some are (or remain) hobbies). My Oxford dictionary show start-up as referring to the

To me "Start-up" always indicated a business (which not all projects are; some are (or remain) hobbies). My Oxford dictionary show start-up as referring to the process of setting (anything) in motion. It goes on to list "a newly established business" as a separate, specific meaning. I think YCombinator is interested in business start-ups. But among hackers like those you'll find in HN... you never know when hobby start-up projects are going to burst out with commercial potential. I suspect that pg et al. appreciate that cross-pollination of "hobby" ideas here has real value for seeding business start-ups.