What's the difference between a startup and a business?

On Quora.com, I site I visit fairly infrequently, someone asked the difference between a business and a "startup." 

Once upon a time, most people would have said, a startup is a young business, just as a baby or infant is a young person.

But things have changed in recent years, and we're all getting smarter about the unique role and needs of a startup. So here is the answer I submitted:

In the new "lean startup" methodology, a startup is very different from a business. A business is an organization (or individual) that normally executes a proven business strategy. By contrast, a startup is an organization or initiative in search of a successful business model. 

This approach is useful, because it doesn't demand perfection from a startup; when you acknowledge you are merely searching for the right success formula (rather than simply executing a formal business plan), you are more likely to tolerate mistakes, learn from them, and make changes (or as the kids today say, pivot) sooner to help you become more successful.

You can read the original Quora post here.