CS3:- 'Symbol Definition'

Hi Folks…

I am using CS3 to look at some code. When I select the keyframe and hit the ‘F9’ button the code window opens up. The ‘Actions-Frame’ tab is highlighted and on the left I see a pane divided into two. I am concerned with the 2nd pane that is broken into ‘Current Selection’, ‘Scene 1’ and ‘Symbol Definition’ .

Under ‘Symbol Definition’ I am see the button and movie clip symbols, I recognize them as so based on the iocns. However there is another 2 family of icons which puzzles me. It’s 3 cubes; 2 of them as base (blue and brown) and one on top(blue). The other is the same with an directional arrow on it. What do they icons symbolize?? Hope some one can advise me. Thanks.