Bir Tawil is a big piece of land that is between Egypt and Sudan. Imagine that you and your friend are playing a game with a big toy car, and you both want to play with it. But you can't decide who gets to play with it first. This is kind of like what happened with Bir Tawil. Neither Egypt nor Sudan wanted the land because it doesn't have many resources like oil or water, so they both decided not to claim it.
Now, you might be wondering why they don't just share it like you and your friend could share the toy car. The problem is that countries have rules called borders that say which land belongs to which country. And because no one officially claimed Bir Tawil, it is not part of either country.
People sometimes call Bir Tawil a "terra nullius," which is a fancy Latin phrase that means "nobody's land." It's kind of like if you found a toy on the playground, but nobody was around to claim it, so it's just sitting there waiting for someone to take it. But since Bir Tawil is a big piece of land, it's not that easy to just pick it up and take it away.
Some people think Bir Tawil should be its own country, but that would be really complicated because it's not very big and doesn't have many people living there. Also, it would be hard to decide who would be in charge of the country. So, for now, Bir Tawil remains a very interesting and unique place that doesn't belong to any country.