The gathering of nets from coastlines (6)
I believe the answer is:
social
'the gathering' is the definition.
(social is a kind of gathering)
'of nets from coastlines' is the wordplay.
'of' indicates an anagram (the answer comes from or 'of' the letters).
'from' indicates named letters should be taken away.
'coastlines' with 'nets' removed is 'coalis'.
'coalis' with letters rearranged gives 'SOCIAL'.
(Other definitions for social that I've seen before include "Needing companionship" , "Of people; gathering" , "Public servant caring for the underprivileged" , "Relating to human groups" , "Relating to society" .)