According to the [Ask Ubuntu Help Center](https://askubuntu.com/help) (which I think you were prompted to look at when you signed up __;-)__ ), the following distributions are considered official Ubuntu flavors:

- Kubuntu
- Lubuntu
- Ubuntu Budgie
- Ubuntu Kylin
- Ubuntu MATE
- Ubuntu Studio
- Xubuntu

All of these are on-topic. Honestly, there isn't much difference among these. It's mostly just the desktop environment, themes and certain pre-installed packages.

Since Ask Ubuntu tends to reflect the list of official flavors on the Ubuntu website, you may also want to look there. Chances are, if a new official flavor is named, Ask Ubuntu won't have it immediately.

### Reference

- https://ubuntu.com/desktop/flavours
- https://wiki.ubuntu.com/UbuntuFlavors