Laws of Thermodynamics
The Zeroth Law There are four laws of thermodynamics which build upon each other. They are numbered 0 through 3 because the most fundamental law was discovered after the First Law had already been given the number 1. Therefore, they had to assign the most fundamental law the number 0. The Zeroth Law simply says there is no heat flow between objects that are the same temperature. In essence, the Zeroth Law is just a definition of what temperature is.