AskDefine | Define available

Dictionary Definition

available adj
1 obtainable or accessible and ready for use or service; "kept a fire extinguisher available"; "much information is available through computers"; "available in many colors"; "the list of available candidates is unusually long" [ant: unavailable]
2 not busy; not otherwise committed; "he was not available for comment"; "he was available and willing to accompany her" [syn: uncommitted]
3 convenient for use or disposal; "the house is available after July 1"; "2000 square feet of usable office space" [syn: usable, useable]

User Contributed Dictionary



  • SAMPA: /@'veI.l@.b(@)l/
  • /əˈveɪ.lə.b(ə)l/


  1. Having sufficient power, force, or efficacy, for the object.
    This is an available plea.
  2. Such as one may avail one's self of; capable of being used for the accomplishment of a purpose; convertible into a resource.
    We have an available candidate.
  3. Readily obtainable.
    The list shows the available products in the store.



having sufficient power or efficacy; valid
  • Hungarian: érvényes
  • Portuguese: válido
ready for use
  • Finnish: käytettävä, käytettävissä oleva, saatavilla, käsillä
  • German: verfügbar, disponibel
  • Hungarian: rendelkezésre álló
  • Polish: wolny
  • Portuguese: útil
  • Swedish: tillgänglig
readily obtainable
  • Czech: dostupný
  • Finnish: saatavilla oleva
  • German: verfügbar, disponibel
  • Greek: διαθέσιμος
  • Hungarian: kapható
  • Polish: dostępny
  • Portuguese: disponível
  • Russian: доступный
  • Swedish: tillgänglig

Extensive Definition

For the thermodynamic function availability, in the sense of available useful work, see exergy.
For availability as a form of cognitive bias, see availability heuristic.
In telecommunications and reliability theory, the term availability has the following meanings:
1. The degree to which a system, subsystem, or equipment is operable and in a committable state at the start of a mission, when the mission is called for at an unknown, i.e., a random, time. Simply put, availability is the proportion of time a system is in a functioning condition.
Note 1: The conditions determining operability and committability must be specified.
Note 2: Expressed mathematically, availability is 1 minus the unavailability.
2. The ratio of (a) the total time a functional unit is capable of being used during a given interval to (b) the length of the interval.
Note 1: An example of availability is 100/168 if the unit is capable of being used for 100 hours in a week.
Note 2: Typical availability objectives are specified either in decimal fractions, such as 0.9998, or sometimes in a logarithmic unit called nines, which corresponds roughly to a number of nines following the decimal point, such as "five nines" for 0.99999 reliability.
Source: from Federal Standard 1037C in support of MIL-STD-188


The most simple representation for availability is as a ratio of the expected value of the uptime of a system to the aggregate of the expected values of up and down time, or
A = \frac
If we define the status function X(t) as
\begin 1, & \mbox t\\ 0, & \mbox \end
therefore, the availability is represented by
E[X(t)]=X.\Pr[X(t)=1] \quad t > 0.
Average availability must be defined on an interval of the real line. If we consider an arbitrary constant c, then average availability is represented as
A_c = \frac\int_0^c A(t)\,dt,\quad c > 0.
Limiting (or steady-state) availability is represented by
A = \lim_ A(t).
Limiting average availability is also defined on an interval (0,c] as,
A_=\lim_ A_c = \lim_\frac\int_0^c A(t)\,dt,\quad c > 0.


Availability is well established in the literature of stochastic modeling and optimal maintenance. Barlow and Proschan [1975] define availability of a repairable system as "the probability that the system is operating at a specified time t." While Blanchard [1998] gives a qualitative definition of availability as "a measure of the degree of a system which is in the operable and committable state at the start of mission when the mission is called for at an unknown random point in time." This definition comes from the MIL-STD-721. Lie, Hwang, and Tillman [1977] developed a complete survey along with a systematic classification of availability.
Availability measures are classified by either the time interval of interest or the mechanisms for the system downtime. If the time interval of interest is the primary concern, we consider instantaneous, limiting, average, and limiting average availability. The aforementioned definitions are developed in Barlow and Proschan [1975], Lie, Hwang, and Tillman [1977], and Nachlas [1998]. The second primary classification for availilability is contingent on the various mechanisms for downtime such as the inherent availability, achieved availability, and operational availability. (Blanchard [1998], Lie, Hwang, and Tillman [1977]). Mi [1998] gives some comparison results of availability considering inherent availability.
Availability considered in maintenance modeling can be found in Barlow and Proschan [1975] for replacement models, Fawzi and Hawkes [1991] for an R-out-of-N system with spares and repairs, Fawzi and Hawkes [1990] for a series system with replacement and repair, Iyer [1992] for imperfect repair models, Murdock [1995] for age replacement preventive maintenance models, Nachlas [1998, 1989] for preventive maintenance models, and Wang and Pham [1996] for imperfect maintenance models.
available in German: Verfügbarkeit
available in Estonian: Käideldavus
available in Esperanto: Havebleco
available in French: Disponibilité
available in Italian: Disponibilità
available in Dutch: Beschikbaarheid
available in Japanese: 可用性

Synonyms, Antonyms and Related Words

abandoned, accessible, adaptable, all-around, approachable, at hand, at leisure, at liberty, at loose ends, attainable, attendant, close by, come-at-able, convenient, deserted, disengaged, fallow, findable, forsaken, free, getatable, gettable, godforsaken, handy, idle, immanent, immediate, in view, indwelling, inherent, jobless, leisure, leisured, lumpen, nearby, obtainable, of all work, off, off duty, off work, on board, on call, on deck, on hand, on tap, open, open to, otiose, out of employ, out of harness, out of work, penetrable, pervious, present, procurable, reachable, ready, securable, tenantless, to be had, to hand, unemployable, unemployed, unfilled, uninhabited, unmanned, unoccupied, unpeopled, unpopulated, unstaffed, untaken, untenanted, untended, vacant, versatile, within call, within reach, within sight
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