Line on desktop with icons below it

I have no idea what it is i do from time to time but suddenly there will appear a horizontal line about two inches from the bottom of my screen. Below the line will be a couple of document icons maybe or perhaps a programme icon. This is not the dock bar. It is further below. It is not launchpad, It is not mission control.

This happened in all three version of Mac OS i have had and i am now on mavericks and a day or two ago the same happened.

When i tap one of the little icons, it brings the docuemnt up.

It is not a fault, but some little known feature I suspect!

Anyone else ever seen it? I contacted an apple agent and they didnt know what it was for either.

Tx