What is a false flag attack?

Attacking the enemy while dressed in their own uniforms or using their own equipment, so that the attack isn't noticed until it is already underway $-$ for example, German pilots flying captured British bombers to attack London in World War II

An attack in which two sides each back a side of another conflict, so the superpowers can fight without directly engaging each other $-$ for example, the Korean War

An attack in which a government or similar entity performs an attack on its own interests, and then blames another group for it $-$ for example, the Nazi attack on the Gleiwitz radio station at the beginning of World War II