Why does Buddhism use the word "realm" when describing one of the different races?

Why is this word used? It's very confusing and makes it sound like you are reborn into a world and not as a different race of being or a human again? Like saying "rebirth in the human realm" to me could sound like I am reborn as an animal and live among humans. Why not use the word races or species to described the 6 options of rebirth?