[1] According to the FIA Formula One regulations, the area must be sufficiently large and secure so as to prevent unauthorised access to the cars, while allowing technical checks to take place.
Essentially, cars in this area must not be touched by anyone without express permission of the FIA stewards.
As such, teams cannot make major set-up changes between qualifying and race day.
The only exception is due to a change in climatic conditions, where the Race Director will give teams permission to make appropriate changes to their cars, or in the case of serious accidents compromising the integrity of the car.
[2] In duathlon (run–bike–run) and triathlon (swim–bike–run) competition the parc fermé is a secure area where bikes are stored during the race.