A question asked once of a single participant is termed a "Question Impression". If there are ten participants in a group which is asked a single question, then in total there have been ten Question Impressions. If there are three questions asked of the same group of ten participants, then there have been thirty Question Impressions.
Note that Question Impressions depend on participants logged in at the time that the question was asked. If a participant joins an activity late, then Question Impressions will not count that participant for those questions asked prior to his joining.