Startup means high scale business with the aim to build new technology and/or test new business model at the beginning. Beginning where you have nothing, you only loose and stress a lot, you are not sure what do you do, what works and what doesn't.

As soon as you returned investors all the money (ROI) in at least x3 amount and you have profitable business, e.g.

• you have a stable profit (income + n > expenses)
• you can live without any investments
• you can pay big salaries to all employees and yourself
• and you still have own resources to keep developing the company and do R&D

you are no more a startup.

At the end it depends on your own definition of a startup. There is no clear standard of what startup is. If startup for you means keep moving forward, changing yourself and innovating, then you may be a startup forever.

I'm not quite sure if Airbnb can still be called a start-up, but I catch your drift.

Well, a start-up stops being a start-up once it has discovered a repeatable business model. The key word here is repeatable.

When it stops taking money from venture capital and starts generating it's own profits.