A gravity assist, also known as a gravitational slingshot, is a spaceflight maneuver that uses the gravity of a planet or moon to change the speed and direction of a spacecraft. By flying close to a celestial body, the spacecraft can gain energy from the body's motion, allowing it to travel faster or alter its trajectory without using additional fuel. This technique is often used in interplanetary missions to save time and resources. For example, the Voyager spacecraft utilized gravity assists from Jupiter and Saturn to reach the outer planets more efficiently, demonstrating the effectiveness of this method in space exploration.