What is a Mommy?

Today Abbey posed this question to me and it kind of caught me off guard. When she woke up from her nap, we were cuddling and she looked up at me and said, "You're my Mommy." I said that yes, I was her Mommy. Then she looked at me and asked, "What is a Mommy?" I thought for a moment. Before being blessed by adoption, I would have probably said something about giving birth etc. Obviously, this couldn't be part of the definition this time(at least not regarding me).  I thought for a moment and then said something about a mommy being someone that loves and takes care of her children. Later today I recalled this conversation. I wondered if there was something else I should have said?  I know that right now she has no concept of the difference between born and adopted. I don't think we've actually ever told her she was adopted. We've told her we went to China to get her. She told Greg this weekend that she was born in Chongqing, China, and that it was a really cool place. So, she knows that. From today's question, though, I realized that I really need to get my thoughts together so I will know what to say when the time comes.