Deprecation is the discouragement of use of something human-made, such as a linguistic term, a proper name, a feature, design, functionality, piece of code, or practice. Typically a thing previously used is deprecated because it is—or is claimed or thought to be—inferior compared to other options now available. Deprecation is thus a mechanism for future improvement. Deprecation implies that the community (generally, or a community of experts, or a professional body governing a sector or industry) has determined that future use—of the term, name, device, design, or feature—is unwise. However, it also means its replacement or removal is not required or is non-urgent.

Something may be deprecated even though past or extant applications of it might still be useful or functional in particular contexts—the goal here need not be the complete replacement of that which has been deprecated but rather an improvement on some broad metric (eg, safety) of the stock of that thing over time. Thus: deprecation of archaic terms to obtain consistency and readability in language/terminology; deprecation of obsolete electrical components to improve safety and compatibility in the housing stock; or deprecation of certain shared code to improve an open-source software project.

Deprecation typically implies or foreshadows a phasing out, a withdrawal or removal from availability, or a discontinuance of use or support, at some time in the future.

In general English usage, the verb "to deprecate" means "to express disapproval of (something)". It derives from the Latin deponent verb deprecari, meaning "to ward off (a disaster) by prayer".

An early, documented usage of "deprecate" in the relevant sense is in Usenet posts in 1984, referring to obsolete features in 4.2BSD and the C programming language. An expanded definition of "deprecate" was cited in the Jargon File in its 1991 revision, and similar definitions are found in commercial software documentation from 2014 and 2023.

Deprecation is an improvement mechanism commonly used in software development, particularly where projects involve a large community of users or coders, or have long or complex development histories, or are rapidly iterating (thus generating more supersedence).

While a deprecated software feature remains in the software, its use may raise warning messages recommending alternatives or 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 a new standard.

Notable reasons for deprecation include: