Bug fix

A patch is a piece of software designed to update a computer program or its supporting data, to fix or improve it. This includes fixing security vulnerabilities and other bugs, with such patches usually called bugfixes or bug fixes, and improving the usability or performance. Although meant to fix problems, poorly designed patches can sometimes introduce new problems (see software regressions). In some special cases updates may knowingly break the functionality, for instance, by removing components for which the update provider is no longer licensed or disabling a device.

Patch management, is a part of lifecycle management, and is the process of using a strategy and plan of what patches should be applied to which systems at a specified time.

Patches for proprietary software are typically distributed as executable files instead of source code. This type of patch modifies the program executable—the program the user actually runs—either by modifying the binary file to include the fixes or by completely replacing it.

Patches can also circulate in the form of source code modifications. In this case, the patches usually consist of textual differences between two source code files, called "diffs". These types of patches commonly come out of open-source projects. In these cases, developers expect users to compile the new or changed files themselves.

Because the word "patch" carries the connotation of a small fix, large fixes may use different nomenclature. Bulky patches or patches that significantly change a program may circulate as "service packs" or as "software updates". Microsoft Windows NT and its successors (including Windows 2000, Windows XP, Windows Vista and Windows 7) use the "service pack" terminology. Historically, IBM used the terms "FixPaks" and "Corrective Service Diskette" to refer to these updates.

...
Wikipedia