Unicorn

"A unicorn startup is a company that's been in business for under ten years, isn’t publicly listed, haven’t been acquired by a third party, and become valued at 1 billion dollars or more worldwide. It gets its name from the mythical animal, thanks to Aileen Lee, founder of Cowboy Ventures, who coined it in 2013 when referring to tech companies that had been valued as much without being having gone public".

Source: https://www.santander.com/en/stories/unicorn-startups