Yup, pinging and detonation. Very bad for...well, everything. Don't allow it. If you hear it, back off the throttle. Ensure you are up to date on all the usual maintenance if the car is all stock, and/or see a specialist if it needs a "tune" if it is modded out. Also, check for fuel quality (switch stations, always run Premium, etc.).
I was riding with my wife in her Saab Turbo, I kept yelling at her because it was pinging so badly...looks like a bad boost control solenoid in conjunction with poor quality gas...it also needed a fuel filter badly, and after changing the filter it improved, and was nearly eliminated with better gas. Cleaning the BCS cured the rest.