Help A strange tab

[Devention]

I received my Note 2 a few days ago and so far it's lived up to, and exceeded all my expectations. This morning I was doing a bit of email deleting in Gmail and it froze for a split second and now I have this tab on the side of my screen that is ever present. I can move it around i.e. t o the top, bottom or either side, but I haven't got a clue how to get rid of it. If I touch the tab a line of icons slides out down the length of the screen.

Is anyone able to shed some light on what this damn thing is and how I can get rid of it?

 

[Devention]

Here's a screenshot for reference, you can see it half way up the left hand side.

 

[ODog2323]

That'll bring up the multi window feature. If you tap it to open an app list you can drag any 2 of those app icons onto the screen to use both apps running st the same time. Hold dowm the back button to make the tab appear or disappear.