Absolute zero is the lower limit of the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reach their minimum value, taken as 0.
An equator of a rotating spheroid (such as a planet) is its zeroth circle of latitude (parallel).
The Fahrenheit scale is a temperature scale based on one proposed in 1724 by Dutch-German-Polish physicist Daniel Gabriel Fahrenheit (1686–1736).
The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid at atmospheric pressure.
A prime meridian is a meridian (a line of longitude) in a geographic coordinate system at which longitude is defined to be 0°.
0 is the integer between −1 and +1, and the numerical digit used to represent that number.