Definition

Entropy is the measure of disorder in a system, a thermodynamic quantity representing the unavailability of a system's thermal energy for conversion into mechanical work. It is the inevitable drift from order into chaos.

In software engineering, it manifests as the thermodynamic tax on every line of code you write—a constant, invisible force destructuring the ecosystem you built.

Example

To move a car, we burn gasoline. We get kinetic energy, but we also produce heat and nitrogen oxides. The waste is the price of the movement.
To ship a feature, we burn cognitive energy. We extract focus from the human brain, but we also produce stress and burnout. The wear on the engineer is the price of the code.