Only Canonical products are considered LTS (Mint does not have this). Their
scheme is to release twice a year, April and October. All releases have
numbers that are significant. The number before the decimal is the year and
the number after is the month. So 10.04 was released in April, 2010 and
10.10 is in October, 2010. The next release is in 11.04, next April. All
releases also have a code name that also follows a pattern. It is
alphabetical and alliterative with the first word being a descriptor and the
second an animal. 10.04 was Lucid Lynx, 10.10 was Maverick Meerkat and the
next will be Natty Narwhal. People shorten it to the descriptor and not the
animal.

LTS releases come out every two years. Regular releases are every six months
except when it coincides with LTS. 10.04 was LTS. The previous one was 8.04
and the next will be 12.04. LTS means long term support and it has three
years of support for desktop and five years for servers compared to 18
months for regular releases. You can upgrade from LTS to LTS and skip
regular releases, but you cannot skip releases if you upgrade regular
releases. However, you do not have to upgrade. You can run any release till
it expires and re-install. LTS is considered to be more stable, but it isn't
really. It is just is less agressive in the type and number of changes. The
same testing process takes palace. However, upgrades for LTS are usually set
to LTS by default whereas regular releases default to regular release. This
allows LTS users to only upgrade essential parts, usually security upgrades,
etc. The down side of LTS is that you are virtually stuck in time form three
years. It will begin to show its age after a time. You can improve this by
enabling the backports which allow you to run newer versions of many
applications on the older version. More information than you asked, but I
write this for lurkers who did not ask but wonder.