Unicorn

With many unicorn IPOs getting listed in 2019, one question is "what is a unicorn?"

Wikipedia states:
Unicorn is a privately held company valued over $1 billion. The term was coined after the mythical animal due to the statistical rarity of such successful ventures.

NYTimes in an article on March 28, 2019 (day before the Lyft IPO) https://www.nytimes.com/2019/03/28/business/startups-ipo.html?action=click&module=Top%20Stories&pgtype=Homepage has an observation about why some startups with high valuations stay private for long.

"Some industry groups and investors who urge fewer regulations say the emphasis on the private markets is an outgrowth of the Sarbanes-Oxley Act, the federal law passed in 2002 that tightened accounting rules for public companies after the accounting scandals of the early 2000s."