A dike is like a big wall that people build to protect themselves from water. You know when you build a sandcastle on the beach and the waves come and smash it down? That's what a dike tries to stop from happening. But instead of sand, a dike is made from dirt and rocks and sometimes even concrete.
When people live near the ocean or a river, they can be at risk of flooding when the water gets too high. So what they do is build a dike along the edge of the water. The dike is usually shaped like a big hill and it goes along for a long way. Sometimes it's only a few feet tall, but other times it can be over 10 feet tall!
When they build the dike, they dig a big trench in the ground first. Then they put a layer of dirt and rocks in the trench, making sure it's packed in tightly. They do this over and over until the dike is the right height. Sometimes they even put concrete blocks in the dike to make it even stronger.
Once the dike is built, people can feel safer knowing that it will help protect their homes and businesses from flooding. But it's important to remember that even with a dike, there is still a chance that water can get over it or around it. So it's always a good idea to be prepared and listen to any warnings from authorities if there is a risk of flooding.