It's simply when someone isn't quite sure what their sexuality is, often thanks to how hard it is for some to label themselves when they just assumed that they were the "default" until that point. Hence questioning; it's just self-searching and education about sexuality to help themselves understand.
I guess that explains it enough. Sorry if that was a annoying question. I just wanted to be able to grasp the meaning a little better. At first I though it was people in the "denial" phase.
