I'm just starting to learn Korean, but I learned pretty quickly that "ajumma" refers to an older woman. It doesn't seem to have any particularly positive or negative connotations, but for Isaac and me, it's become synonymous with "mean, scowly old lady who will trample you to death if you get in her way."
For some reason, the Seoul subway system is always full of ajummas wearing the same outfit. I've come to recognize and respect the "ajumma uniform"; whenever I see a purple visor heading toward me, I get out of the way fast.
I know what you're thinking: "I want to inspire that kind of fear on the subway, but how? How can I dress like a mean subway ajumma?"