Assignor estoppel

Okay kiddo, let's say you have a toy that you really love playing with. You let your friend borrow it for a little while and they play with it too. But then, when it's time to give the toy back to you, your friend decides they want to keep it instead.

Well, in the grown-up world, sometimes people have something called a patent. That's like a special paper that says they made a really cool invention and no one else can copy it without their permission.

Now, let's say the person who got the patent decides to sell it to someone else, kind of like how you might sell your toy to someone else if you don't want to play with it anymore. When they sell the patent, that's called an assignment.

But here's where it gets tricky. If the person who originally got the patent (the assignor) tries to sue someone for copying their invention, they might not be allowed to do that. That's because they already gave up the patent by selling it to someone else. It's kind of like how you can't ask for your toy back from your friend once you've sold it to someone else.

That's what we call assignor estoppel. It's a rule that says the person who sold the patent can't later turn around and say that someone else is copying their invention. They gave up that right when they sold the patent.