In the law, the difference is whether it's a job or not. This is spelled out to a large degree by the IRS. Because of the tax deductability of business expenses, they had to solve that fuzzy line.
It has to do with whether you are trying to make a profit.
Making money for 3 out of 5 years is considered proof. But they consider ow much money is being made, esp. as a percentage of income, the percentage of time you put in, etc. It's complex.
So, an office worker making maybe 50k a year getting $10 on the side every month after investing like 40 hours of driving would probably not count.
In practice, they reduced the number of cars of the road. Uber increases that number.