In this document, the term reliability is used in two quite different senses. It has been used in a qualitative sense to mean the effectiveness or goodness of the system and also in a quantitative sense to mean the probability of failure-free operation for a specified period of time. In the latter sense, it is one of a set of what might be termed reliability characteristics of a system, with other reliability characteristics being Mean Time To Failure (MTTF), Mean Time To First Failure (MTTFF), failure rate, availability and so on. In this section, a method is given for obtaining system MTTF and failure rate from system reliability.