This is when no crime, no matter how big or small, will be ignored or overlooked. It is often used when talking about racism, sexism or drug-taking.
Our school has a zero tolerance policy on drug-taking. If you are caught, you are expelled.
Remember that you wonâ€™t do yourself any favours if you simply throw these idioms into conversation during your IELTS interview. You must practice using them appropriately before the exam.