Emission

Emission is a word that originally comes from Latin. Originally it means something that is sent out. Several things can be sent out:

 The most common use talks about emission of toxic gases. Those gases get produced by factories and motors, like motors in cars.
 People talk about radio emissions. Those are programmes that people can listen to if they have a radio receiver.
 There could be emissions of loud noise, someone might be making loud noises.
 There also are emissions of light.