The process of applying a software patch or update to an older version of software than the update was initially intended for. Backporting most frequently refers to a fix for a security flaw applied to an older version of the software that's still supported by the developer, but one that isn't the most recent release of the software. Backported packages running on older Linux distributions are another popular form of backporting.
Depending on the evolution of the software, backporting an update or patch to an earlier version of the software may involve something as simple as changing a few lines of code all the way to undergoing a massive modification process that involves an extensive overhaul of the entire software code. Software developers may take on the responsibility of officially backporting their software themselves, or a backport may be created and released by authorized or unauthorized third parties and users.