ebay: what is "cross site scripting" ?

[GroupC]

Sometimes on ebay I see a small pop-up window at the bottom of the screen with a message saying: "Internet Explorer has modified this page to help prevent cross-site scripting".

I haven't seen this on any other websites, ever - what does it mean? It doesn't seem to make any difference to my use of ebay, and sometimes it appears and sometimes it doesn't.

[MikeDunn]

https://en.wikipedia.org/wiki/Cross-site_scripting