Jumplists are what you get when you right click an icon in the Windows 7 taskbar and they compliment the improved preview thumbnails that you get when you hover over a taskbar icon. Some people confuse the two.
IE: The jumplist will show the websites accessed in IE.
Similarly, if you right click the Word icon, I see a list of most recently opened Word documents, along with the options to open a new instance of Word, pin/unpin the program or close the window:
If you right click an individual item in a jumplist, you get another menu, from which you can do
even more. Right clicking an item in the Word jumplist lets you open the item, edit it, open it as a new item, print the item or copy it. You can also pin an item to this list (so that it will remain here instead of being replaced by more recent items) or remove it from the list.
Finally, you can open the item’s Properties here, without opening the item itself.
You can also specify the number of recent items that you want to display in the jumplists. Just right click the taskbar, select Properties, and click the Start Menu tab. Click the Customize button and in the Customize Start Menu dialog box, down at the bottom, set the number of recent items to display, from 0 to 60
You don’t have to use the right mouse button to open the jumplists. Another way to do it is to hold down the left mouse button on the icon and then drag it upward (if your taskbar is docked at the bottom of the screen), downward (if it’s docked at the top) or sideways toward the middle of the screen (if it’s docked vertically on either side).  Different applications contain different items in their jumplists.

More:
Jump Lists are lists of recently or frequently opened items, such as files, folders, tasks, or websites, organized by the program that you use to open them. In addition to being able to open recent items using a Jump List, you can also pin favorite items to a Jump List so you can quickly get to the items that you use every day. On the taskbar, Jump Lists appear for programs that you've pinned to the taskbar and programs that are currently running. You can view the Jump List for a program by right-clicking the taskbar button, or by dragging the button toward the desktop. You open items from the Jump List by clicking them.

How to delete the recent items from the taskbar jump lists

Note that the following steps will clear the recent items in all of the jump lists.
Here's how:
Right click the Start button
Select Properties
Click the Start Menu tab
Uncheck the item "Store and Display Recently Opened Items in the Start Menu and the Taskbar"
Click Apply
When you do this, Windows will empty the %UserProfile%\Recent folder, which is where these items are stored. If you want Windows to start saving items again, go back and recheck the box. Also note that this will not delete items that you have pinned to a jump list.