Tax noncompliance（日本称为脱税，台译租税逃漏，大陆译税收不遵从，有北美华文报章译做不遵守税法）泛指一些不利于国家税收的行为，当中包括避税和逃税。

避税（tax avoidance）是通过合法方式减轻或避免税负的手段；逃税（tax evasion）是通过非法方式减轻或逃脱税负的手段。节税（tax mitigation）和税务筹划（tax planning）跟避税意义相同，但较具正面意思。偷税(tax dodge)跟逃税意义相同，但负面意思更重。一般来讲，逃税是设法逃脱「已经产生」的待付税款，而避税是通过合法途径变构交易来「避免产生」可能的税负。

Tax noncompliance is a range of activities that are unfavorable to a state's tax system. This may include tax avoidance, which is tax reduction by legal means, and tax evasion which is the criminal non-payment of tax liabilities. The use of the term 'noncompliance' is used differently by different authors. It's most general use describes non-compliant behaviors with respect to different institutional rules resulting in what Edgar L. Feige calls unobserved economies. Non-compliance with fiscal rules of taxation, gives rise to unreported income and a tax gap that Feige estimates to be in the neighborhood of $500 billion annually for the United States.