Final answer:
Entropy refers to a normal process leading to system decline. It is a measure of a system's disorder and is governed by the second law of thermodynamics.
Step-by-step explanation:
The normal process leading to system decline is entropy. Entropy is a measure of a system's disorder, and according to the second law of thermodynamics, entropy either remains the same or increases in every process. This is because there is an extraordinarily small probability of a decrease in entropy, based on the larger number of microstates in systems with greater entropy. Therefore, entropy is a natural tendency in isolated systems, leading to system decline.