A nebulizer is a medical device that transforms a liquid medication into a fine mist. Other components of a nebulizer include a medicine cup and mouthpiece. The medicine cup is what holds the liquid medication and the mouth piece directs the medicine into the lungs to be inhaled. The compressor is the actual machine itself and is also known as an aerosol delivery system. The compressor unit is available in portable and "plug in" builds. The portable compressor is powered by a battery and can be used even when electricity is not availble. The battery will need to be charged and cannot power the compressor infinitely. The electric compressor must be plugged into an electric outlet in order to be used. It is a good idea to have an electric and a battery operated compressor on hand in case of emergencies. Without a compressor, you can not use a nebulizer. Without a nebulizer, you can not use your compressor. They are both required to deliver the medicine as a mist to your lungs.