band ‧ wag ‧ on /ˈbændˌwæɡən/ BrE AmE noun [countable]
1 . an activity that a lot of people are doing:
The keep-fit bandwagon started rolling in the mid-80s.
2 . climb/jump/get on the bandwagon to start doing or saying something that a lot of people are already doing or saying – used to show disapproval:
I don’t want to look as if I’m jumping on a green bandwagon.