Okay, so imagine there is a really important lady in a country. She is a queen, and she is so important that even when she is not the queen anymore, people still think she is very important. When the queen gets very old, she might not be able to do queen things anymore, but people still think she is important.
So, when the queen is really old and not the queen anymore, but people still think she is important, they might call her the grand empress dowager. This is a fancy way of saying that she used to be a queen, but now she is really old and people still think she is important.
Sometimes, the grand empress dowager might still have some power, even though she is not the queen anymore. She might help the new queen make decisions, or she might be in charge of something important. But even if she doesn't have any power, people still think she is very special because she used to be a queen.