「理由」 (りゆう) means "reason." It's used when you want to explain why something happened or why someone did something. You often use it with から (kara) or ので (node) in a sentence. What is the reason for your absence?

「理由」は、物事がそうなった原因や根拠を説明するときに使います。あなたが欠席した理由は何ですか？