Unicorn, meaning a startup or company valued at $1 billion, was first used venture capital investor Aileen Lee in 2013.
“I was trying to come up with a word that would make it easier to use over and over again,” Lee said in an interview. “I played with different words like ‘home run,’ ‘megahit,’ and they just all sounded kind of ‘blah.’ So I put in ‘unicorn’ because they are -- these are very rare companies in the sense that there are thousands of startups in tech every year, and only a handful will wind up becoming a unicorn company. They’re really rare.”
Sources: Welcome to the Unicorn Club - TechCrunch