Do you have toy cars that are different colors and shapes? Tanks are like big toy cars that can drive on the ground and shoot things. Just like your toy cars, tanks come in different colors and shapes too. But they also have different jobs!
Some tanks are meant to protect other tanks or soldiers by shooting at enemies from far away. These tanks are called "heavy tanks" because they are bigger and have more armor.
Other tanks are called "light tanks" because they are smaller and faster. They are used to move quickly and get a good view of the battlefield.
There are also tanks called "medium tanks" which are a good balance between heavy and light tanks.
Finally, there are tanks called "tank destroyers" which are meant to be sneaky and destroy other tanks from far away without being seen.
So just like your toy cars, tanks come in different colors and shapes, but they also have different jobs, which is why we call them different names like heavy, light, medium, and tank destroyer.