Why are companies such as Uber, Airbnb, Snapchat, Dropbox, etc. still called startups?

I was with the CEO of a recently IPO’d company right when they hit 500 employees.  He said to me — “Jason — we’re not a start-up anymore.  I don’t even know when employees start and leave anymore.”

So that’s one way to think of the term.  Maybe > 500 employees you can’t possibly be a “startup” anymore.

But …

I think the definition, like “cloud” or “SaaS” or even “enterprise”, has changed.

Start-up I think means (x) still in disrupter phase — even if a Unicorn — but (y) not once IPO’d.

Airbnb is bigger than Homeaway, the Airbnb 1.0.  It’s disrupted as much as it’s disrupting.  Probably it’s not a start-up anymore then.  Ditto Uber.

Snapchat and even Dropbox I’d argue are still in the disrupting phase.