All Ubuntu is based on Debian Sid or unstable and not testing. Canonical
does the testing and bug fixing. The difference between LTS and regular
releases has nothing to do with the source packages. It has to do with the
length of support. Regular releases have 18 months and LTS has three years
for desktop and five years for server. Because it has three years of support
users can count on a stable base for that length of time.

Generally they are less aggressive about changes made for LTS releases that
regular releases, but there is no set rules. Most users find fall releases
to be more aggressive, but the next spring release turns that on its head.
11.04 will be a radical departure.