What is the term for reliability that varies over time?

The term for reliability that varies over time is known as the hazard rate. This concept refers to the instantaneous rate of failure of a system or component at a given time, which can change based on various factors such as wear, environmental conditions, or usage patterns.

The hazard rate is a crucial part of reliability engineering because it provides insights into how the likelihood of failure evolves as a system ages or as it undergoes certain operating conditions. For instance, a new component might have a low hazard rate, but as it continues to be used and ages, the rate may increase.

Understanding the hazard rate helps reliability engineers develop maintenance strategies, predict failures, and enhance the overall reliability of systems. This allows for better planning of interventions, ensuring that equipment operates safely and efficiently throughout its lifecycle. In contrast, the other terms referenced in the choices convey different meanings; for example, failure rate is a measurement of the frequency of failures, dependability suggests a general attribute of reliability and trustworthiness, and operational reliability focuses on performance during a specified operational period.