standard pressure

https://doi.org/10.1351/goldbook.S05921
Chosen value of pressure denoted by p or p. In 1982 IUPAC recommended the value 105 Pa, but prior to 1982 the value 101 325 Pa (= 1 atm) was usually used.
Sources:
Green Book, 2nd ed., p. 54 [Terms] [Book]
PAC, 1994, 66, 533. (Standard quantities in chemical thermodynamics. Fugacities, activities and equilibrium constants for pure and mixed phases (IUPAC Recommendations 1994)) on page 536 [Terms] [Paper]