the mutual conversion of a particle and an anti particle into electromagnetic radiation as conversion of energy from one form to another
The Brainliest Answer!
Literally, the term "Annihilation" means "Destruction". 

In simple words, when a particle and its anti-particle come in contact each other, they destroy each other and a burst of gamma radiation is released.

It is mostly used in Particle Physics to describe the relations of Particles and the Anti-Particles

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