Question: Where does the label "spam" come from?

It has become more and more common to meet questions as labelled as "Spam". What does this classification mean?
Strangely if you click on the little red flag "Spam" it even seems that you can delete the corresponding question.
Does it mean that some people here have the power to decide if a question deserves to be answered or merits to be put on the trash?
Given that these questions are answered the same way than any other non spam labelled question, why are they labelled as spam?

 

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