The term 'Dark Mark' is a symbol used by the fictional villain Lord Voldemort in the Harry Potter series. The crossword solutions for this term are 'BLOT' (4 letters) and 'SMUDGE' (6 letters). A BLOT is a spot or stain, usually caused by a liquid, while a SMUDGE is a mark or blur caused by rubbing or smearing. Both terms can be used to describe the Dark Mark, which is a skull with a snake coming out of its mouth.