Choose not to participate (3,3)
'choose not to participate' is the definition.
(to opt out of something is to choose not to do it)
This is the entire clue.
(Other definitions for opt out that I've seen before include "Decide not to participate" , "Choose to be excluded" , "Choose not to participate" , "Decline to participate" , "Choose not to do something" .)
'choose not to participate' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for abstain that I've seen before include "Refrain from doing something" , "Cut it out!" , "Deny oneself" , "Choose not to do something" , "Refrain (from drink)" .)