For some Jewish people, there is a special process called ibbur that happens after someone dies. It's like a way for a person's soul to continue on and reach its full potential.
Imagine you have a balloon and you blow it up as big as you can. Now imagine that your breath is like your soul filling up the balloon. When you die, your soul leaves your body and your balloon deflates.
But sometimes, even though the balloon is deflated, there's still some air left inside. That's like ibbur. It's when a soul that has already left the body comes back and enters the body of another person. It's kind of like putting air into a deflated balloon again.
The new person might not even know that another soul is inside them, but they might feel like they're suddenly better at things they weren't good at before or they might have new ideas and thoughts that they never had before. It's like the new person is being helped by the old soul that came back.
Ibbur is a special thing that some Jewish people believe happens to help souls keep growing and learning even after they've died.