What Difference Exists

[foodchain]

Between decay and Annihilation.

[Gilded]

Annihilation refers to the collision of a particle with its antiparticle converting them to photons or other new particles due to opposite quantum numbers. I'm assuming that in this context you mean particle decay. At least one difference is that it doesn't require the interaction of another particle to transform into a new particle as the it's unstable by itself, where as annihilation can happen with stable particles.

[Tom Vose]

Actually, annihilation is also a type of decay.