Once upon a time, a long long time ago, there was a big country called England, and the people who ruled over this country were called the "monarchs" or "kings and queens". One of the most famous and important families of monarchs in England is called the House of Windsor.
This family started way back in 1917 when the royal family decided that they needed a new name for their family because their old name, Saxe-Coburg and Gotha, had a bit of a German sound to it and that wasn't good for political reasons. So the King of England at that time, King George V, decided to change his family name to Windsor after the castle where they lived and loved to spend their time, Windsor Castle.
Since that time, the current reigning monarchs, like Queen Elizabeth II and her family, have been a part of the House of Windsor. They're sort of like the leaders of the family and they are the ones who make important decisions and rule over the country.
But being a part of the House of Windsor isn't just about being in charge. It's also about being part of a big, extended family with lots of traditions and history. They have special ceremonies and events that they attend together, and they wear special clothes and jewelry that are part of their family history.
So that's the House of Windsor! It's a family that has been ruling over England for a very long time and they're named after a castle where they like to hang out. They have lots of traditions and history, and they're really important to the people of England.