A fog lamp is a special light on a car that helps you see better when it's foggy or misty outside. Just like you can't see very well through fog with your eyes, it's hard to see with regular car headlights because the light reflects off the fog and makes it even harder to see.
But a fog lamp is designed to cut through the fog and shine the light on the road where you need it. It's usually a low, wide beam of light that is angled down towards the road to help you see just a little bit better.
It's important to use fog lamps only when it's foggy or misty outside, because they are very bright and can actually be dangerous to use when it's not necessary. So always make sure to turn them off when you don't need them anymore!