Tax avoidance is the legal utilisation of the tax regime to one’s own advantage, to reduce the amount of tax that is payable by means that are within the law.
By contrast, tax evasion is the general term for efforts not to pay taxes by illegal means.
The term tax mitigation is a synonym for tax avoidance. Its original use was by tax advisors as an alternative to the pejorative term tax avoidance.
Latterly the term has also been used in the tax regulations of some jurisdictions to distinguish tax avoidance foreseen by the legislators from tax avoidance which exploits loopholes in the law.