Unexplained sightings (4)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">unexplained sightings</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for ufos that I've seen before include "Supposed spaceships" , "Potential alien craft" , "Mysterious things" , "Initially, official flying saucers" , "Unauthorised traffic from outer space?" .)