Deprecation

In several fields, deprecation is the discouragement of use of some terminology, feature, design, or practice, typically because it has been superseded or is no longer considered efficient or safe, without completely removing it or prohibiting its use. Typically, deprecated materials are not completely removed to ensure legacy compatibility or back up practice in case new methods are not functional in an odd scenario.
It can also imply that a feature, design, or practice will be removed or discontinued entirely in the future.
Etymology.
In general English usage, the infinitive "to deprecate" means "to express disapproval of (something)". It derives from the Latin verb "deprecare", meaning "to ward off (a disaster) by prayer". In current technical usage, for one to state that a feature is deprecated is merely a recommendation against using it. It is still possible to produce a program or product without heeding the deprecation.
Software.
While a deprecated software feature remains in the software, its use may raise warning messages recommending alternative practices. Deprecated status may also indicate the feature will be removed in the future. Features are deprecated, rather than immediately removed, to provide backward compatibility and to give programmers time to bring affected code into compliance with the new standard.
Among the most common reasons for deprecation are:
Other usage.
An example in hardware design is omission of pull-up resistors on unused inputs to a logic gate. This practice may have been acceptable in the past, but has become deprecated because faster clock speeds are likely to induce more transient noise on input lines, causing hardware glitches or malfunctions.
A building code example is the use of ungrounded ("2-prong") electrical receptacles. Over time, these older devices were widely deprecated in favor of safer grounded ("3-prong") receptacles. The older, ungrounded receptacles were still permitted in many places by "grandfathering" them in existing electrical wiring, while prohibiting them for new installations. Thus, though ungrounded receptacles may still be available for legal purchase in a location where they are obsolete, they would generally be intended only for repairs to existing older electrical installations.
In writing and editing, usage of a word may be deprecated because it is ambiguous, confusing, or offensive to some readers. For example, the words "sanction" and "inflammable" may be misinterpreted because they have auto-antonymic or self-contradictory meanings; writing style guides often recommend substituting other words that are clearly understood and unambiguous. Some word usages that have acquired different connotations over time, such as "gay" or "colored", may be deprecated as obsolete in formal writing.
In technical standards, use of a certain clause may be discouraged or superseded by new clauses. As an example, in the Ethernet standard IEEE 802.3-2012, Clause 5 (Layer Management) is "deprecated" by Clause 30 (Management), except for 5.2.4.
The term "deprecated" may also be used when a technical term becomes obsolete, either through change or supersession. An example from paleontology is the previously deprecated term "Brontosaurus"; before being re-recognized as a unique genus, it was considered a popular, yet deprecated, name for the genus "Apatosaurus". Some examples of deprecated terms from medicine include "consumption" (tuberculosis), "grippe" (influenza), and "apoplexy" (stroke). In chemistry, the international standards organization IUPAC (International Union of Pure and Applied Chemistry) has deprecated the term "methyl ethyl ketone", and now recommends using the term "ethyl methyl ketone" instead.