Crowd inside Guantanamo Bay (3)
I believe the answer is:
mob
'crowd' is the definition.
(mob is a kind of crowd)
'inside guantanamo bay' is the wordplay.
'inside' indicates a hidden word.
'MOB' can be found hidden inside 'guantanamo bay'.
(Other definitions for mob that I've seen before include "Unruly lot" , "Crowd round" , "Crime syndicate or disorderly crowd" , "An undisciplined gang of people" , "Large, disorderly crowd" .)