Why do software companies now use 'hotfix' to describe a planned maintenance outage? Not so 'hot' to me.
In release engineering and management, hotfix means a completely different thing then live update. If you read the wiki definition, it is a little biased and uneducated as to the use of the term. In the 20 years I have heard/used the term, it has never meant live update, as software has not, until recently supported live updates (and as such, software adopted the term "Live Update" to encompass such an update).
So, just a quick definition trainer for you:
Install: The package or process for downloading (the act of retrieving software from a remote device or system to a local device or system) and assembling an application (single entry point executable with or without support files and other multi-entry point executables) or suite (multiple single entry point executables with associated files) on a computer operating environment (ussually based on OS, but can also imply emulated devices, or connected services/mediums).
Update: the package or process for downloading and modifying an existing application, suite, or collection of applications. This can include Upgrades, Service Packs, Patches, HotFixes, and can also be a live update.
Major Release: Typically identified as a new Major version (requirement by MSI, if MSI is used as the install engine). Includes new APIs, SDKs, or major functional shifts or designs. A Major update is typically shipped as a Remove and Re-Install package. Typically keeps user settings and preferences.
Service Pack: A collection of patches and hotfixes rolled into a single update to take a system (application, suite, collection of applications) from any point from it's base up to a specific point. This is also known as a cumulative update.
Patch: An update to a system to bring the software from a known base to a new point, typically identified by new features, collection of Hotfixes/bug fixes, but typically the environment for the application stays the same, as well as the base functionality, and User Interface (though, they may have minor changes to accompany the other fixes that were applied). The scope and level of change associated with a Patch are usually identified by the project manager. As well, they typically need to fit within a specific rule-set of the installation software (e.g. for MSI, no removal of features or components, all files removed must be identified, and accounted for in the patch process, the installation interface can not have significant changes, and no large scale component change, such as major Merge Module updates, or API changes, without the risk of damaging the installation package already installed).
HotFix: An update to the system that is only altering existing files or functionality to correct issues within the current system. Should not have major functional changes. Typically does not have new features or functions.
Live Update, any type of update that can be performed on a system, without the need to restart the system involved. These are typically seen as server side updates on a client/server application. But self-healing applications are a current design paradigm that leading developers and software engineers have been researching. However, that type of technology is not available in most consumer software (there are some fringe developers and engineers that have incorporated it into their applications, and IBM is currently the leader in this area with dozens if not hundreds of patents on differing implementations related to self-healing software).
I hope this clears up some of the confusion around the use of the term Hotfix.
(My references to MSI are simply just that, a reference. As it is currently the most used Install Engine used, however, from what I can tell, it is either not used, or only used for the initial installation of Final Fantasy, and typically doesn't play well with other install/update mechanisms).