A chemical standard usually used for reporting the properties of compounds/molecules.
Generally written in one of the following ways:
0°C or 273.15°K
760 mm Hg or 1 atm
It is used to describe a substance at....
Pressure: 1 atm; 760 mmHg; 101,300 pascals
Temperature: 0°C, 32 F, 273.15 K (kelvin)
It is often used to describe gasses.
At STP one mole of gas will occupy 22.4 liters.