In
reliability theory and
reliability engineering, the term
availability has the following meanings:
- The degree to which a system, subsystem or equipment is in a specified operable and committable state at the start of a mission, when the mission is called for at an unknown, i.e. a random, time. Simply put, availability is the proportion of time a system is in a functioning condition. This is often described as a mission capable rate. Mathematically, this is expressed as 100% minus unavailability.
- The ratio of (a) the total time a functional unit is capable of being used during a given interval to (b) the length of the interval.