Parc fermé
Parc fermé conditions freeze a car's setup from the start of qualifying until the race, so what a team qualifies with is what it races.
Once the rules apply, teams may do little more than routine maintenance: no changes to wings, suspension or ride height. The point is to stop a car being qualified in a low-drag trim it could never race, and to stop an arms race of overnight rebuilds between Saturday and Sunday.
What is still allowed matters as much as what is not. Tyres change, fuel goes in, brake bias is a driver control rather than a component, and a damaged part can be replaced with an identical one. What cannot change is the car's fundamental configuration — which is why a team that has misjudged the weather forecast is stuck with the wing it chose on Saturday.
Breaking parc fermé is permitted, but it costs the grid slot: the car starts from the pit lane instead. Teams sometimes take that deliberately when a weekend has gone badly enough that starting last with a better setup is worth more than the position they qualified in, and it is a common sight after a driver has crashed out of qualifying.
It also explains a particular kind of Saturday evening drama. A car found to breach the regulations after qualifying cannot simply be adjusted back — the breach has already happened, and the penalty follows.