Samudra is a fancy word that describes a big body of water, like an ocean. Imagine you are in your bathtub, but instead of just a small amount of water, you are swimming in a really, really, really big bathtub that goes on for miles and miles and miles. That's a samudra! It's filled with all kinds of creatures like fish, whales, and maybe even mermaids, and it's so big that you can't see all the way to the other side. People use boats to travel on samudras, and they can spend weeks or even months exploring all the different parts of the water. So, a samudra is really just a giant bathtub for all the sea creatures in the world!