What is a Debian based distro?

A Debian derivative is a distribution that is based on the work done in Debian but has its own identity, goals and audience and is created by an entity that is independent from Debian. Derivatives modify Debian to achieve the goals they set for themselves.

Is Ubuntu Debian based or RedHat?

Ubuntu is based on Debian (a very famous and stable Linux OS), but RedHat has nothing like this. Ubuntu package manager file extension is . deb (which uses other Debian based OS i.e. Linux Mint), whether RedHat package manager file extension is .