Wait, the word startup is defined as a scalable subset of small business?

Paul Graham:

A startup is a company designed to grow fast. Being newly founded does not in itself make a company a startup. Nor is it necessary for a startup to work on technology, or take venture funding, or have some sort of "exit." The only essential thing is growth. Everything else we associate with startups follows from growth.

There's actually several competing definitions of startup, from Steve Blanks "An organization in search of a business model" to the dictionary "A newly created business". However, the common silicon valley parlance is that a startup is a business created for growth and scale.