Ajumma in Korean refers to a married woman or a middle-aged lady, but it has a deeper meaning than that. These women are often mocked or considered a threat because of their tendency to be aggressive or self-centered, mostly in public places. 

Cr: http://koreajoongangdaily.joins.com/news/article/article.aspx?aid=2964272

I don’t like to go to grocery shops with Ajumma at all…