Rocket boosters are devices that increase the velocity of a rocket by providing additional thrust. They are crucial in increasing the rocket's speed and helping it reach its destination in a timely manner. Boosters can be attached to the rocket during launch or be built into the rocket itself. They are usually ignited at specific points during the flight to provide that extra push that propels the rocket forward. Overall, rocket boosters play a vital role in the success of a rocket launch and ensuring that the payload reaches its intended orbit or destination.