We recently acquired an old set of encyclopedia for our family library. While clearing off shelf space we were being assisted by our five year old daughter. She became quite curious and asked 'What is an encyclopedia?' I explained that you could look up things in these books, and learn more about many topics. I offered the example of Hummingbird, and showed her the pictures and text in volume 'H'. After a moment or two of study she said, 'Oh, I get it. It's just like Encarta but in books!'
(From the "Rest" of RHF)