Bug popular dissenting group (6)
I believe the answer is:
insect
'bug' is the definition.
(bug can mean an insect)
'popular dissenting group' is the wordplay.
'popular' becomes 'in' ('in' can mean trendy).
'dissenting group' becomes 'sect' (sect can mean a splinter group or faction).
'in'+'sect'='INSECT'
(Other definitions for insect that I've seen before include "Contemptible person" , "may be attracted to a website?" , "Eg, bee, mosquito" , "Member of the largest class of creatures" , "Invertebrate, often winged" .)