Neither very good nor very bad (4)
(Other definitions for soso that I've seen before include "mediocre" , "Indifferent" .)
'neither very good nor very bad' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for so-so that I've seen before include "Nothing to write home about" , "Tolerable, indifferent" , "Of average quality" , "Native of Seville" , "Fair to middling" .)