The siege minion: bigger, tougher and worth more gold than the others. It comes every third wave, every second wave from 15 minutes, and every wave after 25.
team chat
in full english
Wait for the cannon minion, then recall.
the context
The official name is "siege minion", but everyone types "cannon". "wait cannon" means do not recall before the cannon, its gold is too much to miss; "cannon wave" is the wave that carries it, the one you keep to push or recall on.