Gal is a unit of measurement that we use to measure how fast things are moving. It is kind of like measuring how fast you can run, but instead of using miles per hour, we use gals.
Gals tell us how quickly something's speed is changing. For example, if you're driving a car and you hit the gas pedal to go faster, the car's speed will change. The gal is the amount of change in speed over time.
Think of it this way: imagine you're sitting in a wagon and your friend starts pushing you. At first, you're not moving at all, so the gal is 0. Then, as your friend pushes harder and harder, you start moving faster and faster, so the gal gets bigger and bigger.
Scientists and engineers use gals to measure the movement of things like airplanes, rockets, and even earthquakes. They can use this information to design better technologies and make predictions about how things will move in the future.