Well little one, a mummy is a very old body that has been preserved by ancient people using a special process called mummification. You know how you sometimes keep a flower in a vase with water so it stays pretty? Well, the ancient Egyptians did something similar to keep their loved ones looking almost like they were sleeping even after they had passed away.
They carefully took out all of the organs from the body and cleaned it, then wrapped it up in lots and lots of cloth. Sometimes they even put special amulets or charms in with the body to help protect it in the afterlife.
These mummies are really famous and interesting to archaeologists because they can tell us about life a long, long time ago. It's like getting to peek into history and learn something new!