bar178Bar. Definition: A bar (symbol: bar) is a metric unit of pressure that is defined as exactly 100,000 pascals (symbol: Pa). It is equal to 0.987 atmospheres (101,325 Pa), the unit often used as aBAR-178 - Optical Amplifier from SemiNex Corporation. Get product specifications, Download the Datasheet, Request a Quote and get pricing for BAR-178