I think the key question is really "are you basically ready to turn this into a registered company?" If you aren't, then it's not a startup.
More importantly, you don't "work on a startup". You work on a project, a product, a service, an idea. If you're working on a startup, you're hopefully a consultant of some kind: legal, HR, whatnot.
It's okay to say "I work at a startup." But that's really less than useful information for both you and the person you're talking to. It's about the same value as "I'm an Asian-American." Congrats, you qualify for a scholarship. Cookie? At least say "I'm an engineering major." or "I'm doing mobile."
More importantly, you don't "work on a startup". You work on a project, a product, a service, an idea. If you're working on a startup, you're hopefully a consultant of some kind: legal, HR, whatnot.
It's okay to say "I work at a startup." But that's really less than useful information for both you and the person you're talking to. It's about the same value as "I'm an Asian-American." Congrats, you qualify for a scholarship. Cookie? At least say "I'm an engineering major." or "I'm doing mobile."