Marianne is a symbol of France, kind of like a mascot. She's a lady who wears a hat shaped like a pointy hat and has long, flowing hair. People have been using Marianne as a symbol of France for a very long time, even before France was the country we know today. In fact, some people say that Marianne has been a symbol of France since the French Revolution, which happened over 200 years ago!
Some people think that Marianne represents the values of the French people. She stands for things like freedom, equality, and brotherhood. These are all really important values in France (and in many other countries, too!).
You might see Marianne in lots of different places in France. You might see her on a French passport or on a French coin. She's also on the seals of the French President and on many official documents. Even some French cities and towns have statues of Marianne.
So, in summary, Marianne is a lady who represents France and the important values that are important to the French people. She's been around for a long time and you might see her in many different places in France, like on a coin or a statue.