force per unit area, measured in pascal (Pa)
atmospheric pressure at sea level: ~101325 Pa (1 atm)
types: atmospheric, hydrostatic, osmotic, partial, vapor
hydrostatic pressure increases with depth in a fluid: P = rho * g * h
osmotic pressure drives water across semipermeable membranes in biological systems
governs gas behavior via Boyle's law (P inversely proportional to volume at constant temperature)
critical in engineering: structural loads, hydraulics, pneumatics
measured by barometers, manometers, piezoelectric sensors