1 If a bomb goes off, it explodes: --
His gun went off accidentally.
2 If food or drink goes off, it is not good to eat or drink any more because it is too old: --
3 If a warning device goes off, it starts to ring loudly or make a loud noise: --
5 to happen in a particular way: --
The protest march went off peacefully.
Preservatives are added to prevent food from going off so quickly.
Cream will go off very quickly if it is not kept in the fridge.