0 °Celsius is referring to the temperature at which pure water freezes. Liquid substances freeze at different temperatures based on their chemical composition and impurities and minerals in water, like salt change the temperature at which water freezes. 0 Celsius is equivalent to 32 Fahrenheit.

Other definition:

0 °Celsius is referring to the temperature at which pure water freezes. Liquid substances freeze at different temperatures based on their chemical composition and impurities and minerals in water, like salt change the temperature at which water freezes. 0 Celsius is equivalent to 32 Fahrenheit.