The term for the fear of the number 13 is triskaidekaphobia. This phobia is a common superstition in many cultures, with roots in historical, cultural, and religious beliefs that consider the number 12 as a symbol of completeness and 13 as associated with bad luck or chaos. Many buildings avoid using the 13th floor, and some airlines skip row 13 on their planes. Various theories explain the fear, including its association with the Last Supper, where Judas Iscariot, the betrayer of Jesus, was the 13th guest.