TNT or trinitrotoluene is a compound used as an explosive in making bombs and also for other peaceful purposes.
When TNT explodes the exothermic reaction releases a lot of energy that varies between 4100 J and 4602 J per gram of TNT depending on environmental conditions. The energy released during explosions is commonly expressed in terms of the energy released when a particular quantity of TNT explodes. For this, the energy released on the explosion of 1 kg of TNT has been standardized at 4184 kJ.
If an explosion releases X J of energy it is expressed in the TNT equivalent as X/4184 g of TNT. One megaton of TNT refers to a release of energy equivalent to that when 10^12 g of TNT explodes. This is equal to 4.184*10^15 J.