Question

What is atmospheric pressure? How is it caused?

Answer 1

​​​​​​the pressure exerted by the earth'satmosphere at any given point, beingthe product of the mass of theatmospheric column of the unit areaabove the given point and of thegravitational acceleration at thegiven point.
a value of standard or normalatmospheric pressure, equivalent tothe pressure exerted by a column ofmercury 29.92 inches (760 mm) high,or 1013 millibars (101.3 kilopascals).
Atmospheric pressure is caused by the weight of the Earth's atmosphere. Air weighes about 0.08 pounds per cubic foot at the Earth's surface. So, simplistically, every foot of air above you presses down with a weight of 0.08 pounds.