Informal name (7)
I believe the answer is:
moniker
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">informal name</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that informal name can be written as moniker)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for moniker that I've seen before include "Handle" , "common name" , "Nickname" .)