Depends a bit on the context and if you're using that as a formal business phrase or not. I'll assume that you are. In that case, "fiscal freedom" is the degree of freedom an American has from the tax burden placed on that individual by the government. The Heritage Foundation, a conservative think tank organization, has come up with a formula to determine the Fiscal Freedom Index, in which the top tax rate percentage for individuals, the top tax rate for corporations and tax revenue overall as a percentage of national GDP are crunched into a formula.
I've provided a link to the Foundation's site which explains it more in depth.