# Can two photons annihilate?

This is a question about definitions. When two photons interact to create an electron/positron pair, does this process 'count' as annihilation of the photons? I've struggled to find a good definition of the term. Some places say that annihilation requires the end state to be electromagnetic radiation. But, on the other hand, I have found several text books which give annihilation processes ending in hadrons.

• "The resulting annihilation is thus not a direct result of the photon coupling and is a distinct event." ? The simplest $\gamma\gamma\to f\bar{f}$ diagram is just the time reverse of the usual annihilation diagram. I can't think of any reasonable way to not think of this as an annihilation process. – Michael Oct 23 '13 at 23:53