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.

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