I'd already covered that here: http://www.paulgraham.com/wealth.html
To pull directly from the article a technology startup is "measurement and leverage, where measurement comes from working with a small group, and leverage from developing new techniques."
If I pull from chunks I come up with:
A small group of people inventing a new way to solve a difficult problem that is hard for others to duplicate.
Is that far off from how you would sum it up?
So basically they are just a business.