Regular Grandma

We were discussing our plans for the evening. It's Grandma's birthday today, (HAPPY BIRTHDAY!) so we were planning to go to her house for dinner and cake. Nathan and Rylan were talking about it in the other room and I was listening. I heard Rylan explain the details to Nathan and Nathan's question was, "We're going to Regular Grandma's house?" Now I didn't understand what he meant by that question, but Rylan didn't skip a beat he said, "Yeah, not Great-Grandma, just Grandma."