Whaling is when people go out on boats to try and catch big, huge sea animals called whales. People used to hunt whales a lot because their meat and blubber (which is a big layer of fat) can be used for food, oil, and all sorts of things that people need.
But now we know that whales are special animals that are really important to the ocean and its ecosystem. Also, some kinds of whales are in danger and might become extinct (meaning they will disappear from the world forever)!
So, it's not good to hunt whales anymore. Many countries made a law that people can't do it, but some people still do it illegally. It's important to protect and care for our whale friends in the ocean.