The Kursk Magnetic Anomaly is a place in Russia where there is a really strong magnet hidden deep underneath the ground. Think of a really powerful magnet like the one that sticks your fridge notes and pictures, but much much bigger! This magnet is so strong that it changes the way the magnetic field (a force that attracts magnetized objects) behaves in that particular area.
Scientists discovered this anomaly using special instruments that can measure magnetic fields. They found out that the magnetic pull in that area is much stronger than in other parts of the world. That's why it's called a "magnetic anomaly."
People are very curious about the Kursk Magnetic Anomaly because it's the biggest one on Earth that we know of! Scientists study it to try and figure out why it's there and what it does. Maybe someday we will find out more about it!