1. Quashing a decision means nullifying or cancelling a decision that has been made.
2. It essentially renders the decision as if it never happened and removes its legal effect. For example, if a court quashes a decision made by a government department, it means that the decision is no longer valid and cannot be enforced.
3. Quashing a decision can be done through a legal process, such as an appeal, in which a higher court or authority reviews the original decision and decides to overturn it.