STP

Abbreviation for standard temperature (273.15 K or 0 °C) and pressure (10 5 Pa); usually employed in reporting gas volumes. Note that flow meters calibrated in standard gas volumes per unit time often refer to volumes at 25 °C, not 0 °C.
See also: standard conditions for gases
Source:
PAC, 1990, 62, 2167 (Glossary of atmospheric chemistry terms (Recommendations 1990)) on page 2217