Half our technical calls start with the same mix-up: a customer says they need "4 bar", the datasheet says "40 metres", and nobody is sure whether that is good news or bad.
Head and pressure are the same physical thing measured two ways. Head is the height of a water column; pressure is the force that column exerts. The conversion is a single line:
10 metres of head ≈ 1 bar. More precisely, 10.2 metres of water gives 1 bar at sea level. So 40 metres of head is about 4 bar, and a pump advertised at 55 m delivers roughly 5.4 bar at zero flow.
Why manufacturers prefer head
Metres of head do not depend on what you are pumping against: lift, pipe friction and back-pressure all subtract from the same budget. Pressure numbers tempt buyers to think of "4 bar at the tap" without accounting for the 30 metres of lift and the pipework in between. Head forces you to count the whole system, which is exactly what correct sizing needs.
Next time a datasheet confuses you, divide by ten. You will be within a few percent of the truth, and closer than most quotes you will ever receive.