Debian is a GNU/Linux distribution. The name comes from the founder of the project, Ian Murdock, and his wife, Debra. Hence "Deb" and "Ian".
If you use Debian, you tend to love Debian. Why?
Often imitated, never beaten.
There are some reasons not to like Debian, the most obvious of which is that the "stable" distribution, while historically very stable, achieves this by being up to three years 'out of date'. Ubuntu, a derivative of Debian, addresses this by having regular (six-monthly) release cycles. Also, Debian has a mentality of "we have official packages for everything", meaning that $new_thing has to be uploaded into the repository before you can get it. However, more people are packaging things in third party repositories that you can add to your AptSourcesList, and you can always install things from source.
Read about the different FlavoursOfDebian.
The Debian PackageManagement format is .deb. See DebianPackaging on how to create these, or DebianPackageTools for how to use dpkg(8)/APT/other programs that install .deb packages.
See NewZealandLinuxMirrors for places in NewZealand to get Debs/ISOs.
There are a LOT of great Debian web pages on the internet. Here are but a few...
Part of CategoryDistribution and CategoryDebian
154 pages link to Debian: