Comment by jltsiren
Tax avoidance and evasion are not distinct categories. Some things are clearly legal. Some things are clearly illegal. And for many things, the legality can only be determined by a court after the fact.
Laws are inherently ambiguous. There is no objective classification that tells for each possible action whether it is legal or illegal. That's why courts and lawyers are needed.
"Tax avoidance and evasion are not ..."
Those are formally defined terms here in the UK [citation needed - must find one].
Tax avoidance is avoiding paying a tax by following some legally sanctioned rules. For example, in the UK, using an ISA, which is a form of bank savings account, for which the interest is paid tax free. ISAs were created by an Act of Parliament. By saving in an ISA you avoid paying some tax.
Tax evasion is avoiding paying tax ... by not paying tax that is due, according to the law of the land.
There are no grey areas these days. When you do "Self Assessment" in the UK, one of the early questions paraphrases to "have you done anything dodgy". I think it is something like: "Have you participated in any tax evasion schemes within the tax year considered here". Without looking it up now (which takes a while), it may even use the word avoidance instead of evasion.
Self assessment is similar to how the US and some other countries do taxation.
In the UK the norm is Pay As You Earn (PAYE). Your employer does everything - you earn a wage and tax (Income Tax and National Insurance) is extracted at source and the balance is paid to you. The taxes are passed on to His Majesty's Customs and Revenue (HMRC). You can fill in a Form P11D if you want to claim expenses for something you supplied or pay for benefits received from your employment. Most employees in the UK don't care about taxation too much - it just happens.
Tax avoidance and evasion are very different beasts. Do be careful.