Atmosphere (atm) is a unit of pressure defined as 101,325 Pa. It represents the average pressure exerted by Earth's atmosphere at sea level.
Pascal (Pa): A unit of pressure equal to one newton per square meter.
Torr: A unit of pressure where one torr is equal to one millimeter of mercury (mmHg).
Ideal Gas Law: $$PV = nRT$$, an equation relating the pressure, volume, amount, and temperature of an ideal gas.