Online stand-in (6)
I believe the answer is:
avatar
'online stand-in' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for avatar that I've seen before include "Incarnation of a Hindu god" , "movie" , "Archetype" , "Bodily form of (Hindu) deity" , "Incarnation of a Hindu deity in human or animal form" .)