Meaning of Bar
All air compressors force air into a confined space where it is stored ready for use. When the user demands the air to drive, for example a tool, the storage unit will open a valve and the air under pressure will flow down the output hose or other connector.
Traditionally in the UK and USA, pressure was measured in terms of psi (pounds per square inch) though in Europe and increasingly also in Britain, the Bar is used.
One Bar equates to roughly standard atmospheric pressure at sea level which in turn is around 14.5psi. So, 1 Bar is approximately 14.5psi.
The pressure the air is stored under is measured and stated. Typically the higher the pressure, the more power the compressor will be capable of delivering although other factors may need to be considered such as the flow-rate (cubic feet per minute or litres per minute).