A patch is a set of changes to a computer program or its supporting data designed to update, fix, or improve it. In the context of Drupal, a patch is a file that contains a list of differences between one set of files, and another. Patches are used to apply bug fixes, security updates, and other improvements to Drupal core and contributed modules.
Patches are created by comparing two different versions of a file, and then creating a file that contains the differences between the two. This file is then applied to the original version of the file, which updates it to the new version. Patches can be created manually, or with the help of a version control system such as Git.
Patches are typically submitted to the Drupal issue queue, where they can be reviewed and tested by the Drupal community. Once a patch has been tested and approved, it can be applied to the Drupal codebase, and the changes will be available to all users. Patches can also be applied manually, by downloading the patch file and applying it to the Drupal codebase.
Patches are an important part of the Drupal development process, as they allow developers to quickly and easily apply bug fixes and security updates to the Drupal codebase. Patches also allow developers to contribute their own improvements to the Drupal codebase, which can then be shared with the rest of the Drupal community.