Quiet moment in corporation, activists quickly dispersing (5,3)
I believe the answer is:
flash mob
'activists quickly dispersing' is the definition.
I can't tell whether this definition defines the answer.
'quiet moment in corporation' is the wordplay.
'quiet' becomes 'sh' (both can be said to tell someone to be quiet).
'moment' becomes 'mo' (as in 'just a mo').
'in' indicates putting letters inside.
'corporation' becomes 'flab' (I can't explain this - if you can you should believe this answer much more).
'sh'+'mo'='shmo'
'shmo' placed within 'flab' is 'FLASH-MOB'.
Can you help me to learn more?
(Other definitions for flash mob that I've seen before include "streakers?" , "Sudden mass of people" , "Unexpected gathering" , "Ad hoc group assembled to do something unusual in a public place" .)