Facebook’s decision to buy the ‘no revenue’ Instagram for $1 billion created quite a stir in the market. What exactly Facebook plans to do with Instagram is not very clear, but Zuckerberg defended his decision by claiming that the number of Instagram users had reached a ‘tipping point’ from where it would grow significantly.

What is a tipping point? Going by definition per se, a tipping point is a sociological term that means a critical mass or the threshold beyond which it is difficult to stop the flow of a ‘change’ that started progressing but at a crawling pace. This change is usually irreversible or uni-directional; it can be both for the good and for the worse.

A recent article Help Wanted! Silicon Valley’s hiring crunch in BBC Business News wrote,

Just 18 months ago, Tango was just another unknown scrappy venture trying to make it in Silicon Valley. But, within 10 days of introducing its free mobile video-calling service for smartphones over 3G, 4G and wi-fi, Tango amassed a million users.

This is what I call a tipping point in a startup. In this example it is the launch of free mobile video-calling service.