Like some online videos (5)
I believe the answer is:
viral
'like some online videos' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for viral that I've seen before include "Go ___ (take off via the internet)" , "(Of video) fast spreading" , "Like pathological agents" , "Spreading rapidly" , "Pertaining to an ultramicroscopic infection" .)