PG put it best in his essay "Startup = Growth"[1]:
"Let's start with a distinction that should be obvious but is often overlooked: not every newly founded company is a startup. Millions of companies are started every year in the US. Only a tiny fraction are startups. Most are service businesses—restaurants, barbershops, plumbers, and so on. These are not startups, except in a few unusual cases. A barbershop isn't designed to grow fast. Whereas a search engine, for example, is."
A barbershop is a great example of a small business. A barbershop is obviously different in nature from a search engine because it's not designed for rapid growth.