Source : Webster's Revised Unabridged Dictionary (1913)

Interrogation \In*ter`ro*ga"tion\, n. [L. interrogatio: cf. F.
   interrogation.]
   1. The act of interrogating or questioning; examination by
      questions; inquiry.

   2. A question put; an inquiry.

   3. A point, mark, or sign, thus [?], indicating that the
      sentence with which it is connected is a question. It is
      used to express doubt, or to mark a query. Called also
      {interrogation point}.

Source : WordNet®

interrogation point
     n : a punctuation mark (?) placed at the end of a sentence to
         indicate a question [syn: {question mark}]