Venturi vacuum generators use compressed air to create vacuum. They can be used to transport certain fluids and powders, eg flour, sawdust, or even food products. As they do not require electricity, they can be safely used in hazardous environments.
An air compressor takes air from the atmosphere into an intake port, and using mechanical means (pistons, screws, rotary sliding vanes) pushes that air into a smaller area, thereby increasing the pressure. Air compressors can be sized all the way from the extremely powerful that could supply a large factory, to ones that can just drive small pneumatic tools.
Vacuum pumps are used in a variety of applications from manufacturing processes to medical devices. Vacuum pumps convert mechanical energy into pneumatic energy by evacuating the air contained within a system.