Definition of Dark mark

The Dark Mark, in the Harry Potter book series, is the symbol of Lord Voldemort and the Death Eaters. It looks like a skull with a snake coming out of the mouth in place of the tongue. It is summoned using the incantation Morsmordre. While unknown at the time, the summoning of the basilisk by Tom Riddle in Harry Potter and the Chamber of Secrets may have been the inspiration for the Dark Mark. The basilisk emerged from the mouth of the statue of Salazar Slytherin in the Chamber of Secrets.