When you have a split-brain, it means that the two sides of your brain (the left side and the right side) can't communicate very well with each other. It's like they're two separate brains that don't talk to each other a lot.
This can happen if you have a certain kind of surgery where doctors cut the connection between the two sides of your brain. They do this to help people who have seizures and other problems that start in one side of their brain and spread to the other side.
When your brain is split, it can make some things hard for you. For example, if someone shows you a picture in your right eye (which sends information to the left side of your brain), you might be able to say what the picture is. But if they show you the same picture in your left eye (which sends information to the right side of your brain), you might not be able to say what it is.
This is because your left brain is usually in charge of talking and understanding language, while your right brain is usually better at understanding things like pictures and colors. So if you only see something with your right eye, your left brain can figure out what it is and tell you. But if you only see it with your left eye, your right brain has to figure out what it is and tell your left brain, which is harder to do.