Ahhhhhh

Yeah, I was so confused but knew that they probably had mistranslated a title lol. But... what is it supposed to be? Do you know?

Nope, I have no idea lol

In the original it is written as 빈 마마 = "bin mama". If you translate it just like that it means "empty mama".
But in the Joseon Dynasty they didn't use the name of each person but Styles or Titels (King, Queen, Crown Prince, ...) with this they could differentiate the rank. "bin" (빈) is such a title and simply means Concubine, "mama" (마마) means mother, so the right translation would be "concubine mother"
They call them mother bc the rightful Queen of the King is the mother of the whole nation and the Concubines should also devote themselves to the nation.

I hope I could be of help a little bit ⁄(⁄ ⁄·⁄ω⁄·⁄ ⁄)⁄

Ohhhhh, I see, thank you so much for explaining!

You're welcome (●'◡'●)ﾉ