STP stands for Standard Temperature and Pressure. As the name entails, STP refers to “normal” conditions at sea level.
STP refers to a temperature of 0˚C and pressure of 1 atm.
STP is important in science because scientists often perform experiments at STP in order to get consistent results. Just know that when you see STP, it refers to 0˚C and 1 atm.
Chemistutor 