Unit for pressure. As a rule of thumb: 1 bar is approximately the air pressure on the earth's surface or the hydrostatic pressure of a water column 10 m high. In other countries, the units PSI or kg/cm2 are commonly used.

PSI = pound-(force) per square inch = unit of pressure commonly used in the USA

[https://de.wikipedia.org/wiki/Pound-force_per_square_inch]

1 psi ≈ 0.069 bar

1 bar = 14.504 psi

[Wikipedia / Further explanation: https://en.wikipedia.org/wiki/Bar_(unit)]