If you are making untaxed money, then you are most likely self-employed, and you are therefore a business (regardless of whether or not you are set up as an LLC/Corporation or have a business license). 

The incentive to make a profit is what separates a business from a hobby. You don't have to actually make a profit in order to be a business, but there should be a chance of making a profit, big or small. 

Your business must make a profit in 3 years out of 5 consecutive years.