Ok, I’m feel like an idiot, but what is Windows clipboard?
Don't feel like an idiot. The only stupid questions are the ones that go unasked.
It's a temporary file where anything you cut or copy is kept until you paste it somewhere or until you cut or copy something else.
The exploit here is that a FLASH presentation (Frequently used to put moving advertisements on websites) uses a command to place a malicious URL (web address) into the clipboard in hopes that the victim will then paste it into a browser and wind up at a malicious website.
Macs also use a clipboard file for the same purpose.