In general, reliability (systemic def.) is the ability of a person or system to perform and maintain its functions in routine circumstances, as well as hostile or unexpected circumstances. The IEEE defines it as ". . . the ability of a system or component to perform its required functions under stated conditions for a specified period of time." Reliability may refer to:

Reliability engineering ensures a system will be reliable when operated in a specified manner

Reliabilism in philosophy and epistemology

Reliability theory, as a theoretical concept, to explain biological aging and species longevity

Reliability (statistics), of a set of data and experiments

Reliability (computer networking) is a category used to describe protocols.

Data reliability, a property of some disk arrays in computer storage.

High availability or uptime is the reliability of physical telecommunication networks, computers, and many other types of equipment