Folgerphobia is the fear of the number 13, specifically related to its association with bad luck and superstitions. This phobia can manifest in various ways, such as avoiding the 13th floor in buildings or refraining from activities on the 13th day of the month. The term combines "Folger," referring to the fear of the number, and "phobia," which denotes an irrational fear. It is part of a broader category of numerophobia, which encompasses fears related to numbers in general.