What differentiates a startup from a normal business? A standup desk?
More specifically, we normally think of startups as businesses where you can do the work once and then sell it multiple times, while in a normal small business or consulting shop, you have to do the work for each customer. There's a pretty big grey area - enterprise software companies often need a significant amount of customization for each customer, while with the sharing/gig economy, whether you can "do the work once and sell it multiple times" depends on whether you consider "the work" to be the service the customer is paying for or the service of connecting an independent contractor to potential customers. But it seems to work pretty well as a functional definition.