ability of an item to be in a state to perform a required function under given conditions at a given instant of time or over a given time interval, assuming that the required external resources are provided
NOTE 1 This ability depends on the combined aspects of the reliability performance, the maintainability performance and the maintenance support performance.
NOTE 2 Required external resources, other than maintenance resources do not affect the availability performance of the item.
NOTE 3 When referring to the measure for availability, the preferred term is 'instantaneous availability'.
NOTE 4 Adapted from IEC Multilingual Dictionary: 2001 edition.