I hadn't seen this yet. It's a Blizzard post that I found linked from a story on the Worldofwarcraft.com home page about today's small patch (1.10.1) .
These are the different types of patches:
To provide better communication with our players, we would like to inform our community about the various methods used to update World of Warcraft. The following are the four major methods of updating the game:
Content patch - The content patch introduces major additions and/or changes to the game, whether in terms of functionality, content, economy, social interaction, or combat. For example, we recently opened up the dungeon Maraudon, as well as adding the priest spell Prayer of Fortitude as part of the same content patch. Content patches require a maintenance period of several hours and are accompanied by a download and patch notes.
Hotfix - A hotfix is a change made to the game deemed critical enough that it cannot be held off until a regular content patch. Hotfixes require only a server-side change with no download and can be implemented with no downtime, or a short restart of the realms. Because there is no download component to a hotfix, there are no downloadable patch notes. Instead, we will announce hotfix information through the forums, the in-game message of the day, and in the Server Alert window on the login screen.
Minor patch - A minor patch is identical to a hotfix, with the exception that a minor patch requires a download and will be accompanied by patch notes.
Localization patch - The game is currently translated into three languages with plans to introduce more. While not often, there are times when we must make changes to text within the game to accommodate the various languages, and this takes the form of a localization patch. Localization patches, when they occur, take place across all language versions of the game and are accompanied by a download and patch notes. Oftentimes, bug fixes will also be included with a localization patch to better utilize the downtime. These bug fixes will be documented in the patch notes as well.
We hope that this information provides more insight to our players regarding the update process, and in the future, we will use this guideline in order to keep our players informed on the World of Warcraft update process.
Direct link to the sticky post.