Having more than five fingers or toes. Use the tag extra finger or extra toes if it's the case of an artistic error (earlier versions of AI image generators are especially famous/infamous for getting hands wrong that way), but use this tag when the character is supposed to have them, such as the book version of Hannibal Lecter.
The following tags are aliased to this tag: extra_digit, extra_fingers, and polydactyly (learn more).