The Debian developers have announced that they have decided to extend the support period for the Debian 6 “Squeeze” branch until February 2016.
Normally, the support for this Debian branch should have ended on May 31. Just like with any other distro, the developers would stop pushing patches and users would need to move on. It's not like people couldn't use it, but it wouldn't be as safe.
“This is an advance notice that regular security support for Debian GNU/Linux 6.0 (code name ‘squeeze’) will be terminated on the 31st of May. However, we're happy to announce that security support for squeeze is going to be extended until February 2016, i.e. five years after the initial release. This effort is driven by various interested parties / companies which require longer security support,” reads the official announcement.
This basically means that Debian 6 “Squeeze” will receive five years of support, just like the Ubuntu LTS version. The developers have also explained that squeeze-lts is only going to support i386 and amd64 architectures, and users who are running a different platform will need to upgrade to Debian 7 (wheezy).
Getting a longer support period for Debian 6 “Squeeze” is actually a wakeup call for people who haven't upgraded yet. You can download Debian 7 right now from Softpedia and upgrade.