What does Ubuntu mean by "support" for its releases?

Whenever Ubuntu releases a new version during six months, they offer support for that version for the coming six months right? What does that support mean? Does it mean that I cannot use apt-get to install any more softwares in it once that six months is over?

If that is the case, then is my ubuntu 10.04 of no use to me in installing applications and softwares anymore? If that is not what it means, then what exactly does a 5 year support for an LTS mean?

Solution 1:

It means that you will only be able to get security updates during that period. One it is over, the repositories are closed and moved to an archive.

Apt-get will stop working unless you change your software-sources, and even then no one will fix bugs or security problems.

You can still use an unsupported version, but expect some problems.

You can still use 10.04 until April 2013 in desktops or 2015 in servers. That means that Firefox (and similar packages) won't be updated after April 2013, but Apache and MySQL (for example) will get updates until 2015. You can check the status of each release here.