What is the secret on Harry Potters scar?

Harry Potter's scar is the result of a curse that was placed on him by Lord Voldemort when he was a baby. The curse was meant to kill Harry, but it backfired and instead left him with a scar in the shape of a lightning bolt on his forehead. The scar is a physical manifestation of the connection between Harry and Voldemort, and it is also a reminder of the dark events that occurred on the night Harry's parents were killed.