A pinned site appears as a tiny square icon to the left of your tabs and never goes away, keeping the site open and up to date.
Pinning is easy, but Safari doesn't tell you how to do it — that's where we come in!
If you decide to unpin a site, just drag its icon back to the right of the tab bar to turn it into a regular tabbed page, then click the "x" to delete it as usual.
Top Sites displays thumbnail previews of certain websites, grouped on one page. One way to call up the Top Sites is to click the ‘grid’ icon in the Bookmarks Bar.
After you click the Top Sites icon the Top Sites page is displayed.
I know I could Reset Safari and tick 'Reset Top Sites' but I don't want to loose my current Top Sites positions. As far as I know it's a bug and things get stuck sometimes.
That would take a day or so to re-establish with browsing and pinning. I found the only way to solve it is to load up the Top Sites Page click on the site that is stuck wait for it to finish loading and then hit the little icon (The one that represents Top Sites.) in the Favourites Bar to immediately take you back to the Top Sites Page.