Push-to-pass is a mechanism on a racing car which provides the driver with the ability to increase the car's power for short periods of time, usually via a button on the steering wheel. The system is designed to make overtaking easier and hence make the sport more exciting to watch.

Several racing series have implemented push-to-pass systems, including the former Champ Car

Champ Car

Champ Car was the name for a class and specification of open wheel cars used in American Championship Car Racing for many decades, primarily for use in the Indianapolis 500 auto race...

 series, the A1GP series (who refer to their system as PowerBoost) and the Indy Racing League (who refer to the system as an overtake button).

There is no requirement that the system be used only when attempting to overtake another car. For example, a driver may choose to operate the system in order to defend a position. The amount of extra power, the amount of time it's available and the number of boosts available during the race varies from series to series.
In Formula One Racing the kers ( kinetic energy recovery system ) is used to increase maximum speed for overtaking.