(Not the OP) I've read PG's article, and it makes sense, but it narrowly fits YC's model and leaves out lean, bootstrapped companies. For that reason, I prefer Steve Blank's definition: "An organization in search of a repeatable, scalable business model". There's a good discussion here: http://www.quora.com/What-is-the-definition-of-a-startup
You're far too concerned with a (buzz)word that loosely fits many, many businesses and definitions and isn't as exclusive or elite or prestigious as you may feel.
