Tax avoidance is a legal way to avoid or reduce the tax payed to the government or state. It contrasts with tax evasion, which is illegal dodges to avoid paying tax. A tax shelter is one type of tax avoidance. Tax havens are places which offer low tax.
The World Bank's World Development Report 2019 on the future of work says governments should curb tax avoidance. It remains a fact that tax avoidance is the way many companies and rich people manage to pay as little tax as possible.