The terms used to describe the characteristics of a failure include hidden, predictable, preventable, and random.
A hidden failure results in a complete loss of function without being evident to the operating crew under normal circumstances. This typically applies to protective devices that are not fail safe. (Examples: emergency systems and standby plants and equipment.)
A predictable failure displays some evidence, at an early stage, of the potential for failure, and a reasonable estimate of the time interval before full functional failure occurs.
A preventable failure includes a reliable time interval or usage, such as number of cycles, before functional failure occurs.
A random failure refers to a failure that occurs at any time and is not constrained by time or usage.