Why are there such things like 2nd or 4th queen? I'm confused... Shouldn't other girls of the king be called concubines???
It’s partially because during the Goryeo Dynasty women were much more equal to men than during the Joseon Dynasty; even compared to other parts of the world. For instance, they had equal inheritance rights as men, they could get a divorce without being ostracized and adultery was a crime both men and women could commit (wives from less powerful clans and families received the status of concubines).
King Taejo had 29 wives with whom he had 34 children (25 princes and 9 princesses) - out of it there were 6 queens, the rest were concubines. The queen status was given to the women from the most powerful clans so none of them would be offended.
Gyeongjong (Gwangjong’s son) had 4 queens (and one concubine) - the first queen was a daughter of the last Silla king while the others were the daughters of Wook and Jung, therefore they were either sisters or cousins - so naturally all of them came from the most powerful clans and needed to be given an equal status.