Is unicorn a billionaire?

Excuse me, but could you clarify something for me? I came across the term "unicorn" being used in the context of finance and cryptocurrency, and I'm a bit confused. Is it referring to a company that has reached billionaire status? Or is there a different meaning behind this term that I'm missing? I'd appreciate it if you could explain it to me in a way that's easy to understand. Thank you in advance.