Stampede of the unicorns: will a new breed of tech giants burst the bubble?

Lyft, which went public on Friday, will soon be joined by Uber, Airbnb and other companies valued over $1bn - and they may be just the animal to burst a bubble

Five years ago Aileen Lee, founder of Silicon Valley investor Cowboy Ventures, coined the term "unicorn" for a private company valued at more than $1bn. Back then unicorns were almost as rare as their mythical namesakes - just 39 existed, according to Lee. Now there are 334 around the world, worth more than $1tn. And this week some of the very biggest beasts started stampeding towards the public markets.

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