Okay, imagine that your mommy and daddy are getting married. And imagine that their wedding is super special, like the biggest and fanciest wedding you ever saw.
Now, imagine that there are two different families who also have a wedding, but their weddings are also super special, just like your mommy and daddy's. And they decide to combine their weddings into one big giant wedding.
And because it's so big and so special, people start calling it the "wedding of the weddings". It's like when you combine your favorite toys and your friend's favorite toys and you both play with them together.
So, the wedding of the weddings is when two or more people decide to combine their special weddings into one big, amazing celebration for everyone to enjoy together.