Okay kiddo, let's talk about vassalage.
So imagine you're a king or queen of a big kingdom. You've got lots of people working for you, but it's just too much for you to manage all on your own. What do you do? You enlist the help of some other powerful people who can help you out. These people are called vassals.
Now, let's say one of your vassals is doing a really great job and you want to reward them. You can give them some land to control. This is called granting them a fiefdom. Your vassal now becomes a lord or lady and has their own little section of your kingdom to manage.
But let's imagine you're not the only king or queen in the world. There are other kingdoms out there too. And those kingdoms also have their own vassals. Your vassal might also have vassals working for them! These are called sub-vassals.
So now your vassal, who is a lord or lady, has their own sub-vassals working for them. It's like a big chain of people working for someone else.
This is what we call multiple vassalage. It's when one person has vassals working for them while they themselves are also a vassal of someone else. It can get pretty complicated, but it all comes down to people working together and helping each other out!