So. 2 Arbiters, 1 Overlord, 1 Osiris, 1 LABC, 2 HFBCs and some reavers against 1 carrier, 1 overlord, 2-3 LABCs is a gank.
Ok.
Edit; Oh. Sorry, there was a gunboat too!
Edit 2: 1 Heavy BS (carrier), 1 LABC vs 1 light bs (Osiris) and 1 LABC in a system full of asteroids while the second party kept hugging a pob is a gank too.