Triskaidekaphobia is the fear or avoidance of the number 13. The term comes from the Ancient Greek words "treiskaídeka" meaning thirteen and "phóbos" meaning fear. It is also a reason for the fear of Friday the 13th, called paraskevidekatriaphobia or friggatriskaidekaphobia. The origins of the phobia are unclear, but it may have come from Norse mythology, which tells how the god Odin invited eleven of his closest friends to a dinner party at his home in Valhalla, only to have his party crashed by Loki, the god of evil and turmoil, thus giving a total of 13 people. Many ships, hotels, buildings, and elevator manufacturers have avoided using the number 13 for rooms and floors based on triskaidekaphobia.