Unicorns may be the stuff of legend. But they're real. Sort of ... and they're on the rise.

A unicorn is the term given to a privately owned company worth an estimated $1 billion or more. The name was coined by an American venture capitalist, on account of how rare they were.

But they're not so rare anymore – the Confederation of British Industry says there are at least 390 unicorns globally, worth a combined $1.2 trillion.

China and the US battle for the top spot, with more than 100 unicorns each. The UK is home to 14 – by far the most in Europe. France has three and Germany has two.

Tech companies dominate the UK list, from pharmaceuticals to food delivery and banks to artificial intelligence. But there are other examples outside that sphere.

Take Brewdog, for example. It is one of Scottish city Aberdeen's biggest exports.

This craft beer empire was started by two friends and their dog just 12 years ago. They got money through crowdfunding and now the business is worth $2.2 billion.

"Did we catch the crest of the wave? Were we in the right place at the right time?" muses Karl Ottomar, Brewdog's head of production, as he explains the company's meteoric rise.

The company is known for its Punk IPA, and named its crowdfunding drive Equity for Punks. Ottomar says: "Crowdfunding is basically giving people an opportunity to buy shares and become part of the business. So – equity for punks.”Adding: "It's not a fad. It's totally in the blood ... there's pride, there's a belief, there's a real love and ownership of the beers and I think that's quite special in terms of wanting that and making that grow more. It's an obsession."

When asked where the company goes next, he's ambitious: "Why not two billion or three billion? The sky's the limit. We need to know our markets, we need to be in different markets. There are no limits and the owners and the board are very keen on expanding boundaries. We're on to a big winner in China. And I think for the fantastically curious nature of the Chinese nation to try new things from across the world, I think it could be really interesting. And I think the branding and everything about the branding and the story of where it came from is, I think, going to be really interesting and a real winner."

Russell Borthwick, the head of Aberdeen's Chamber of Commerce, is thrilled to have Brewdog on his patch. For him, this is a real endorsement of the city and just goes to show big businesses can thrive even outside London. 

"I think it gives the business community confidence. It sets a marker, you can run a major global business from this region," he says.

"To actually be able to demonstrate that two guys in a garage with a dog, turning into a global brand ... other people are now thinking 'why not me? I can do that too,'" he says. And he proudly points out: "It's very appropriate that the unicorn is the national animal of Scotland."

To achieve that valuation at all is the stuff many businesses would kill for – to do it in 12 years is a huge achievement.

But there are firms doing it even more quickly, such as Oaknorth, a fintech company based in London, which managed to get past the $1 billion point in a matter of months.

"Oaknorth was built really to help small- and medium-sized business owners get access to financing from banks, which is something that historically banks have been very poor at providing," explains co-founder, Rishi Khosla.

He adds: "We achieved unicorn status in just under two years. I don't think I was audacious enough to have a plan that was that aggressive. We had an aggressive plan, but not that aggressive."

And he denies it detracts from the start-up mentality, adding: "For me, it's a term. It's an irrelevant term for me. What's relevant is where are we going as a business, how are we going as a business, what are the fundamentals as a business, are we actually helping clients, are we helping those business owners scale their own organizations right? That's actually what matters."

For those companies wishing to become a unicorn, Aberdeen University business professor, Ignacio Canales has this tip: "Ambition plays a role. A very cohesive leadership team also helps explain it. When you have people who are driven and want to make the world a different place, they're more likely to become a unicorn ... Invent a business that doesn't exist and you'll become a unicorn."