It's my understanding that you're working on your "startup" until you've found a repeatable way to generate profits. Once that occurs you then begin working on your "company".

Startups focus on high growth. http://www.paulgraham.com/growth.html

I think there isn't an exact definition but generally a startup has theoretical hyper growth potential. So opening your own bakery would not qualify, envisioning a franchise chain of bakeries (or a social network etc.) would.

[I don't particularly like this definition but that is the common understanding AFAIK]