Reliability is a broad term that focuses on the ability of a product to perform its intended function. Reliability can be defined as the probability that an item will continue to perform its intended function without failure for a specified period of time under stated conditions. The product or a system defined here could be an electronic or mechanical hardware product, a software product, a manufacturing process or even a service.
Reliability engineering consists of the systematic application of time-honored engineering principles and techniques throughout lifecycle of an item,product,assembly or a system. Its goal is to evaluate the inherent reliability of a product or process and showcase potential areas for improvement in its reliability. As all failures cannot be eliminated from a design, hence another goal of reliability engineering is to identify the most likely failures and then identify appropriate actions to reduce the effects of those failures.