A universal background check is like when you want to buy a toy at the store and your mom or dad checks to see if you have enough money to buy it, and if you didn't steel anything from the store before. When people want to buy guns, some states make them go through a background check to make sure they are allowed to have a gun. But some states don't do this. A universal background check would mean that everyone who wants to buy a gun in the whole country would have to go through this process, no matter where they live or what kind of gun they want to buy. This helps make sure that people who shouldn't have guns, like criminals or people with mental illnesses, won't be able to buy them.