pressure, \(p\)

https://doi.org/10.1351/goldbook.P04819
Normal force acting on a surface divided by the area of that surface. For a mixture of gases the contribution by each constituent is called the partial pressure \(p_{i}=x_{i}\ p\), where \(x_{i}\) is the amount fraction of the \(i\)th constituent and \(p\) is the total pressure.
Sources:
Green Book,2nd ed., p. 12 (https://www.cintegrado.com.br/site/documentos/green_book_2ed.pdf)
PAC, 1996, 68, 957. 'Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)' on page 987 (https://doi.org/10.1351/pac199668040957)