The main difference between an air compressor and a generator is the type of energy they produce. An air compressor compresses and stores air in a tank for later use, while a generator converts mechanical energy into electrical energy. Air compressors are typically used to power pneumatic tools, inflate tires and other inflatable objects. Generators, on the other hand, are used to produce electrical power, which is useful as a backup power source during power outages or for outdoor activities such as camping.