Literally, “The throne of peril”. The seat at the Round Table occupied by the most senior (or available) Knight of the Order of Avalon within the Earth-40 Brane.
In time of existential threat to humanity, the Pendragon Directive empowers the Knight holding this seat with full authority to avert the threat by any resources required.
The Siege Perilous is dependent on the Geas bestowed by the Dragons Breath.