In engineering in general, reliability is the capacity of a component or a system of such components to perform as designed. See reliability theory and reliable system design. Computer programs exist to quantify complex system reliability using the techniques of reliability modelling.

In telecommunication, the term reliability has the following meanings:

1. The ability of an item to perform a required function under stated conditions for a specified period of time.
2. The probability that a functional unit will perform its required function for a specified interval under stated conditions.
3. The continuous availability of communication services to the general public, and emergency response activities in particular, during normal operating conditions and under emergency circumstances with minimal disruption.

Source: from Federal Standard 1037C in support of MIL-STD-188

See also:

• Reliability engineering
• ilities

In psychology reliable is connected to the consistency of scores. If the same measure is repeated several times, the measure is said to be reliable if we get the same result every time. (provided that what is measured is the same). Notice that reliable have nothing to do with reality! A clock can be reliable (by measuring time in a very consistent way), but at the same time measure the time completely wrong (e.g., The clock is set 1 hour late). In order for reliable to be true, what is measured must be true.

A conclusion is said to be reliable if others come to the same conclusion, using the same premises. In science it is therefore important to show the premises for the conclusion ! Otherwise, it´s bad science!

In psychometrics, reliability is the precision (i.e., freedom from random error) of the scores of a measure; see reliability (psychometric).

In testing, reliability is the extent to which the measurements resulting from a test are the result of characteristics of those being measured. See Reliability for a fuller description.