Daily Serving of Vegetable

I am a student learning the basics of Flash, so bear with me.
What is the vegetable/term/tool used in Flash?

What does it do? Your responses are appreciated.Daily Serving of Vegetable
That would be the onion skin. It shows a range of frames both
before and after your current frame, progressively fading them out
as if they're layered on translucent paper on top of each other, or
''onion-skinned''. By dragging the edges of the greyed out block in
your timeline you can expand or reduce the number of frames
displayed in onion-skin mode, to let you better follow and track
your animation.