The period during which performance parameters are measured.
Note: A performance measurement period is determined by required confidence limits and may vary as a function of the observed parameter values. User time is divided into consecutive performance measurement periods to enable measurement of user information transfer reliability.

A quality, usually quantified by a numerical value, which quality characterizes a particular aspect, capability, or attribute of a system.
Note: Examples of performance parameters are peg count and mean time between failures.

Basic error events or other performance-related occurrences that may be detected by monitoring a digital signal. [T1.503-1996]

The ability of an item to perform a required function under given conditions for a given time period.
Note 1: It is generally assumed that the item is in a state to perform this required function at the beginning of the time interval.
Note 2: The term reliability is used as a measure of reliability performance. [T1.226-1992]

A requirement that specifies a performance characteristic that a system or system component must possess; for example speed, accuracy, frequency [POSIX.0].

A statement of general criteria that define a desired result without specifying the techniques for achieving that result. Synonym performance-based standard. [After X9.19]

In a satellite orbit, the point that is closest to the gravitational center of the system consisting of the primary body and the satellite.
Note: In an orbit about the Earth, periapsis is called perigee. In an orbit about the Moon, periapsis is called perilune, and in an orbit about the Sun, it is called perihelion.

Of a satellite orbiting the Earth, the point in the orbit at which the gravitational centers of the satellite and Earth are closest to one another.

See altitude of the apogee or of the perigee.

A network added between a protected network and an external network, in order to provide an additional layer of security. A perimeter network is sometimes called a DMZ.