A ruling is a statement issued by Konami which clarifies the interactions between cards and card effects. Unofficial rulings are not issued by Konami, but are based on official rulings (e.g. by extrapolating an official ruling on a specific card's effect to include all cards with a similar effect). While it is generally safe to follow such rulings, and they even often influence judges' decisions, Konami does not recognize them and occasionally issues official rulings that contradict them.