Reliability

property of consistent intended behaviour and results

ability of an item to perform as required, without failure, for a given time interval, under given conditions. Note 1 to definition: The time interval duration can be expressed in units appropriate to the item concerned (e.g. calendar time, operating cycles, distance run, etc.) and the units should always be clearly stated. Note 2 to definition: Given conditions include aspects that affect reliability, such as: mode of operation, stress levels, environmental conditions, and maintenance.

Reliability refers to the closeness of the initial estimated value(s) to the subsequent estimated values.