noun
A word or phrase that indicates a particular season, used in traditional Japanese poetry such as haiku and renga. Each 季語 is associated with a specific season and is collected in reference books called 歳時記.
俳句には必ず季語を一つ入れる。
You always include one seasonal word in a haiku.
「雪」は冬の季語だ。
"Snow" is a winter seasonal word.