What are negative pressure, atmospheric pressure and positive pressure?

When selecting micro DC pumps, the process often involves three concepts, negative pressure, atmospheric pressure and positive pressure.
These three concepts correspond respectively represent the rarefied, standard and dense state of gas.
Atmospheric  Pressure: atmospheric pressure means that the gas pressure in the atmosphere of our everyday life. Standard atmospheric pressure is 101325 Pa (Pa Pascal - commonly used as the unit of pressure). 100,000Pa = 100KPa, so we use 100KPa or 101KPa to represent "the standard atmospheric pressure".
Due to different geographical locations, altitudes, temperatures, etc., each location's actual local atmospheric pressure is different from the standard atmosphere. For simplicity, atmospheric pressure can sometimes be approximated as the standard atmospheric pressure, i.e., 100KPa;
Negative: it refers to a pressure which is lower than the ratio of atmospheric pressure. We often call it "vacuum." For example, when drinking with a straw, it's negative pressure inside of the straw. The inside of suckers hanging is also negative pressure.
Positive: it refers to the state that the pressure is higher than the atmospheric gas. For example, when pumping a car or a bicycle tire, it's positive pressure inside of the pump.