Correct me if I'm wrong, but the stem in the 'non-flipped' position is at an accute angle to the stearer tube, thus resembling the angle on a quill stem. When small frames became popular among recreational riders (translation: the rest of us) in order to show lots of seat post and still reach the hoods the stem needed to be turned over to raise the bars. A 'flipped' refers to a stem at an obtuse angle to the stearer -- not that there's anything wrong with that. So as a point of reference...

not flipped:
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flipped:

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