This option allows you to check a detail of your Recycle Bin content (the place where your deleted files usually go and stay for a while in case you want to recover them, also wasting disk space if really don't needed).
If Recycle Bin is empty, you'll see that word next to this option. Otherwise, it shows a brief detail of how many space, in bytes, the Recycle Bin takes and how many items are in there (an item can be a file or a folder). Due to speed reasons, only are reported those items on the root path of Recycle Bin.
Details by Drive
You can get a window, with a detail of space consumed by Recycle Bin for each drive on your computer. Just click the brief detail on menu (the one that specifies Size: nnnnn Items: nnn).
Empty Recycle Bin
Click this option to empty Recycle Bin without warnings/questions.
On the Details by Drive window, you can Right-click the result's box to get more options, like Open Recycle Bin in explorer (this can be donde with a Double-click on result's box too), or copy the result's box text to clipboard.