Question

what is the product of NH4Cl

Answer 1

I'm assuming this is some sort of decomposition reaction. Very likely you'll have ammonia and hydrochloric acid in equilibrium with ammonium and chloride ions since these are conjugate acid/bases and are fairly stable.

Answer 2

Your question should be more explicit (conditions of the reaction). Are you heating it? are you dissolving it in water?

NH4Cl is usually the product of a reaction, not a reactant.
If you are looking for its name, it's 'ammonium chloride'.