The probability that a product, piece of equipment, or system performs its intended function for a stated period of time under specified operating conditions
Four key elements
Probability, time, performance, & operation conditions.
When the product fails right in the beginning. Example; light bulb, replace old one & it doesn't work
Failure after some period of use
1. Failure rate -- number of failures per unit time. 2. MTTF -- Mean time to failure: reciprocal of failure rate, for items that must be replaced. 3. MTBF -- Mean time between failures; for repairable item.