Mottainai Baasan

In the books, the titular Grandma seeks to explore the true meaning of the Japanese phrase "mottainai" after her son asked her what it meant and she couldn't answer. "Mottainai" is a commonly used exclamation that roughly translates to "what a waste!", expressing regret over wastefulness. The Grandma seeks to explore the meaning and importance of "mottainai" in the story.

(Source: Anime News Network)