What is frame breaking?
A frame breaking script is a piece of code on a website that will make sure that it is the frame showing.
It's probably best to show some examples. Google doesn't break frames, as can be seen here:
Our AdF.ly header remains intact.
The following site does break frames:
So you can how the user cannot click the Skip Ad button and continue to their intended destination.
You can use the above URL to test your adverts before you submit them if you are not sure if they break frames.