A graser is like a laser but instead of shooting out light, it shoots out tiny little particles called gravitons. These gravitons are really, really small and are responsible for gravity, which is what keeps us grounded on Earth and what makes things fall when we drop them.
Imagine you have a ball and you want to throw it to your friend who is far away. You can use your arm to throw the ball, but you can't throw it super far because your arm is not powerful enough. Now imagine you have a machine that can shoot out little particles that can carry the ball all the way to your friend. That's kind of like a graser.
Scientists are still trying to figure out how to make a graser that is powerful enough to work in real life. But if they can, it could be really useful for things like space travel, where you need a way to move very quickly without using a lot of fuel.