What is the meaning of the word "pace car"?

Definitions:

  1. A car that leads the racing cars around the track at a safe predetermined speed to ensure that the field remains in order and that the drivers are not racing at full speed until it is safe to do so. copy to clipboard NOUN
    • In NASCAR, the pace car goes 45 miles per hour. copy to clipboard
  2. A vehicle used in motorsport races to control the speed of competing cars on a track, especially at the start of the race or during a caution period such as after an accident or during hazardous conditions. copy to clipboard NOUN
    • The race included seven laps run behind a pace car following heavy rain. copy to clipboard