A central concept of thermodynamics is that of the macroscopic system, defined as a geometrically isolable piece of matter in coexistence with an infinite, unperturbable environment. The state of a macroscopic system in equilibrium can be described in terms of such measurable properties as temperature, pressure, and volume, which are known as thermodynamic variables. These properties are constructs. They may or may not correlate with how we perceive their everyday language equivalents. When a macroscopic system moves from one state of equilibrium to another, a thermodynamic process is said to take place.
Some processes are reversible and others are irreversible.
The laws of thermodynamics, discovered in the 19th century through painstaking experimentation, govern the nature of all thermodynamic processes and place limits on them. What we do is posit forces in order to account for changes in motion. Doing so, leads in various cases to our being able to predict and manipulate phenomena, but there is always the possibility that we are working within specific or 'local' conditions or perceptions which we mistakenly take to be universal, but outside of which our laws either do not apply, or do not give the whole picture. Zeroth Law of Thermodynamics. The vocabulary of empirical sciences is often borrowed from daily language.