What are the differences between an Ubuntu Long Term Support release (LTS) and a normal release?
There is a new release every 6 months (apart from Dapper, which was delayed 2 months). Every two years, the release is a Long Term Support version.
This is what this looks like:
As you can see from the diagram, people who have installed the 8.04 LTS server don't need to worry about replacing it for still another 2 years! Fantastic. :-)
As if this wasn't enough, Ubuntu release an additional version of the last LTS between releases - such as 8.04.1, that incorporates all of the updates up to this point. This is called a Point-Release (or sometimes snapshot). Those are released every quarter to half year, as needed.
In addition to support, there are Development strategies that differentiate an LTS release:
Thanks to Oli for demystifying that last part, I wasn't quite sure about it.
An LTS gets package updates for supported software for 3 years for desktop packages and 5 years for server packages, compared to 18 months support for standard releases. Current to 14.04, Ubuntu LTS gets package updates for supported software for 5 years, compared to 9 months support for standard releases. Current to 14.04, Xubuntu LTS and Lubuntu LTS get package updates for supported software for 3 years.
This means you can guarantee a system for a long time. Applications won't jump versions, so it makes a very solid deployment platform.
Ubuntu syncs with Debian at the beginning of a new development cycle. On a normal release this pulls in packages from debian-unstable, whereas in an LTS cycle, packages come from debian-testing.
These packages have usually had more time with Debian and should therefore reflect a better quality product (albeit at the cost of bleeding edge features).
There is supposedly more focus on bug fixing for an LTS release, whereas an LTS+1 might focus on adding features, LTS+2 focuses on performance and LTS+3 on stability before rounding it off for the next LTS.
This is less formal than the other points as it's frequently ignored.
Canonical provides security updates for the LTS releases for 3 years on the desktop and 5 years for the server version. The normal release is only supported with updates for 18 months.
Previous desktop LTS releases were supported for 3 years.
However, Ubuntu 12.04 LTS will be supported for 5 years both for desktop and server releases.
Simply put, LTS releases introduce fewer new technologies than Normal releases, and replaces them with Long Term Support of the older, more time-tested technologies that have proven track records of working like said.