Pressure defined as 101325 Pa and used as unit of pressure with the symbol atm.
Sources:
CODATA Bull. 1986, 63, 1 (https://doi.org/10.6028/jres.092.010)
PAC, 1996, 68, 957. 'Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)' on page 993 (https://doi.org/10.1351/pac199668040957)