Internet Explorer network developer tools long Gap time

I'm optimizing a webpage. The page takes about 5 seconds to load in Chrome, but 15 seconds in IE11. Viewing the IE developer tools network tab shows that it spends 12 seconds in Gap.

My question is what is Gap and what is being done during Gap? I know it's described as "the time between completion of this request and the page being loaded" in IE, but I'm not sure what is meant by that.