Tax

The more usual terms are tax avoidance and tax evasion, but avoidance = mitigation to all intents and purposes.

Tax evasion is illegal. For example, concealing earnings to reduce income tax can lead to large penalties and jail.

Tax avoidance is legal (but see last paragraph). For example, in the UK married couples can transfer assets between themselves with no capital gains tax effects at all. So, if I owned shares that would make a gain of $20,000 when sold, the sensible thing to do is to transfer half to my wife then for both of us to sell, each making a profit of $10,000. Currently, gains in a tax year of $10,000 would not be attract a capital gains tax charge. If I had kept all the shares and sold them my gain of $20,000 would be well over the exempt limit and I would have to pay CGT.

However, some clever (?) accountants and lawyers have constructed very complex financial schemes to try to avoid tax. In many cases, when the UK tax authorities challenged these in court, the tax authorities won because the only motive of these complex schemes was to avoid tax and they were so artificial that they were classed as evasion.