秋 (あき) means "autumn" or "fall," the season after summer. It's known for cooler weather and colorful leaves. You can say 秋は紅葉が綺麗です (Aki wa kōyō ga kirei desu), meaning "Autumn leaves are beautiful in the fall."

秋(あき)は夏(なつ)の後(あと)で、涼(すず)しくなる季節(きせつ)です。「秋(あき)は好(す)きですか」のように使(つか)います。