Definition:
A "booster rocket" is a type of rocket that is used to help launch a spacecraft into space. It is the first stage of a multistage rocket, meaning it provides the initial thrust needed to lift the rocket off the ground.
"The booster rocket ignited and lifted the spacecraft high into the sky."
In more technical discussions, you might encounter phrases like "solid rocket boosters" or "liquid fuel booster rockets," which refer to specific types of booster rockets based on the fuel they use.
While "booster rocket" primarily refers to a rocket used for space launches, the word "booster" on its own can refer to anything that enhances or increases something, such as a "booster shot" in vaccinations or a "booster club" for school sports.
In summary, a "booster rocket" is an essential part of launching spacecraft into space.