Ad hoc is a Latin phrase which means "for this [purpose]." It generally signifies a solution that has been tailored to a specific purpose, such as a tailor-made suit, a handcrafted network protocol or a specific-purpose equation, as opposed to general solutions. It can also refer to an improvised and often impromptu event or solution "on an ad-hoc basis", as opposed to well-prepared ones.
Ad hoc computer network
In computer networking, ad-hoc is a connection method for wireless LANs that requires no base station — devices discover others within range to form a network for those computers. Devices may search for target nodes that are out of range by flooding the network with broadcasts that are forwarded by each node. Connections are possible over multiple nodes (multihop ad-hoc network). Routing protocols then provide stable connections even if nodes are moving around.
The term ad-hoc network can also refer to an independent basic service set (IBSS).
Ad hoc committee
Ad hoc is also used to describe a particular type of committee; one which is formed to deal with a particular issue, and disbanded after the issue is resolved. These committees provide stop gap or temporary measures to solve problems that are not resolved by ordinary processes of the organization to which the committee belongs. The GATT was controlled by an ad-hoc committee before the WTO was established.
Ad hoc hypothesis
In philosophy and science, ad hoc often means the addition of corollary hypotheses or adjustment to a philosophical or scientific theory to save the theory from being falsified by compensating for anomalies not anticipated by the theory in its unmodified form. Philosophers and scientists are often suspicious or skeptical of theories that rely on continual, inelegant ad hoc adjustments. See Skeptic's Dictionary: Ad hoc hypothesis.
An interesting example of an ad hoc hypothesis is Albert Einstein's addition of the cosmological constant to relativity in order to allow a steady-state universe. Although he later referred to it as his greatest mistake, it has been found to correspond quite well to the theories of dark energy.
Ad hoc pronunciation
Many reference works employ ad hoc pronunciation schemas as a way of indicating how words are pronounced. These are especially popular in US published works, such as the Merriam-Webster dictionary. An example of an ad hoc pronunciation would be "DICK-shun-ary", where the capitalisation shows which syllable is stressed. This is in contrast to systems such as the International Phonetic Alphabet, which attempt to put pronunciation schemas on a scientific footing.
Critics of ad hoc schemas point out that such schemas are inherently self-referential, since they rely on the ability of the reader to already know how a large number of words are commonly pronounced. In addition, such schemas often assume a certain language, dialect or accent on the part of the reader, and due to its popularity in the US, this is very often a US accent.
As its name suggests, there is no "standard" ad hoc schema, and so examples will vary considerably according to the publication's whim. In contrast, the IPA seeks to base pronunciation solely on vocal tract configurations and on the phonemes produced, though very often common simple words are used to illustrate how the IPA applies in a specific language.
Proponents of ad hoc claim that it is much easier to use than IPA, though will often concur that this is usually only because the pronunciation is already known.
Ad hoc querying
Often called ad hoc reporting, this implies a system that allows users to customize a data query (generally from a database) in real time, as opposed to one that limits them to canned (pre-created) reports. For instance, the reporting system may allow you to select the fields to be returned as well as the limiting criteria for the records to be returned. Often ad hoc reporting is structured to enable someone without extensive SQL knowledge to have similar access to the database. Ad hoc reporting systems often provide GUI-based query creation. One pitfall to watch out for with ad hoc reporting is that a user may inadvertently issue a very costly request to the database, a problem less prevalent when using canned reports which are generally created by developers with a better knowledge of the underlying database schema.da:Ad hoc de:Ad hoc es:Hipótesis ad hoc id:Ad hoc he:אד הוק it:Ad hoc lt:Ad hoc hipotezė nl:Ad hoc pt:Ad hoc sl:Ad hoc sv:Ad hoc uk:Ad hoc