When people or groups work hard to win against each other, that's called "competition". "Competition" in business means the idea of companies working to get money and customers before other companies get them.
When companies that sell similar products are competing hard against each other, one way to describe it is to say that the "competition is fierce". "Fierce" means energetic, wild, and maybe a little bit violent. It's usually used to describe animals, but it can also describe the level of competition between two people or companies.