Decals are like stickers you put on things to decorate them or show something important. They are usually made of thin material with a sticky side that you can stick onto different surfaces like walls, cars or even your toys.
Let's say you have a favorite cartoon character and you want to put it on your skateboard. You could buy a decal of that character and stick it on your skateboard. Decals can also be used for safety purposes like putting a reflective decal on your bike helmet to make it easier for cars to see you when you ride.
Sometimes people use decals at work too. For example, people who work on construction sites may use decals to show important safety information like where to wear a hard hat or which way to walk to avoid danger.
The cool thing about decals is that they come in all shapes and sizes, and you can make them yourself or buy them at stores. Just remember to always ask an adult for help when using them!