"I think the're called First Officers"......  

Someone said "I think they are called First Officers", implying they are not Flight Officers.   So, the question is, why are we calling them anything professionally below?   "Hi folks, this is your Captain from the Flight Deck, welcome aboard...."

Why are they being called or recognized as any of the below titles of "Flight Officer" is incorrect, particularly when "officer" is in their title?  

Captain

First Officer

Second Officer

etc

Aviation is borne from the Laws of Admirality, where ship's "officers" are designated.   The Captain is considered the highest "officer" on the vessel, and those under him in command are both his senior officers and junior officers.   In the airlines, they have adopted those same titles even if the FARs don't recognize any of them.

So, using the terms above is incorrect if one thinks junior officer and senior officer is also incorrect for aviations terms.