Startup is a small giant, or a child giant.
They are defined by the market size.
Small businesses usually have a local market (street/city).
The startup market is global.
Hmm, I think this definition needs some kind of innovation factor. Most start-ups try to do something different than the competition. Those who succeed improved or innovated successfully. Small local business mostly innovate on how to do things (process improvements to cut cost), less on the product itself