What do your parents call each other?

This is a very interesting phenomena, I don't know if this happen to everyone, but this happens in my family. That is, my parents never call each other by name, if they need to call the other one, they will normally ask my siblings or I to call. And when they want to refer the other one, they will say the father or the mother. I don't know why is it happening, I also don't know will we be like that in the future and I dare not to ask my parents as well. I guess this must wait until I myself married and fathered a child. So, what do your parents call each other??