Ichthys is a Greek word that means fish. In Christianity, the symbol of the fish is often used because it has a special meaning.
A long time ago, when Christians feared being persecuted for their beliefs, they had to come up with ways to secretly identify themselves to other believers. One day, a Christian drew a simple fish symbol in the sand, and another Christian recognized it and drew another fish symbol next to it.
That's how the symbol of the fish became a secret way for Christians to identify each other. Later on, it became a more popular symbol, and it's still used today in many different forms.
Some people wear jewelry with Ichthys symbols on them or put them on their cars as a way of showing their faith. Some churches even use Ichthys symbols in their logos or as decorations inside the church.
So, Ichthys is just another way for Christians to show their faith and connect with other believers. And it all started with a simple drawing of a fish in the sand.