SnowQueen is the relationship between Regina Mills/the evil queen and Mary Margaret/Snow White being in a romantic relationship. The creator of the ship is fanfic author iamthecreatorofsnowqueen. They created the whole ship not just the name but the whole ship the idea of Regina and Mary Margaret being in a romantic relationship.
SnowQueen represents that even though you disliked someone with some time you will get over it and along the way love will happen. When your enemy becomes your family that's when Regina is truly happy because she and Snow are now a family. snowqueen represents that even though you dislike someone even though there is distrust and betrayal. You can forgive and accept them and the greatest love comes from the struggling journey.