In Urban Dictionary, Ubuntu is defined as
I'm confused about the meaning. How true is this sentence? Are really Ubuntu and Debian so close to each other?
No, this is a joke.
Ubuntu (the word) "is an ethic or humanist philosophy focusing on people's allegiances and relations with each other". It is often translated directly as "humanity towards others. The word has its origin in the Bantu languages of southern Africa".
Ubuntu's goal is to be a user friendly Linux distributions for those unfamiliar with Linux in general. "Ubuntu has a strong focus on usability and ease of installation" whereas "Debian is known for relatively strict adherence to the Unix and free software philosophies" and will sacrifice user friendliness in favour of those ideals.
Hence the formulation of the joke. If you are new to Linux and are unable to configure Debian, you may instead choose Ubuntu. They have taken a inconsequential fact about the Ubuntu distro (it's naming based on an African word) and altered it to poke fun at the project goals, just like advanced users often ridicule beginners (or newbies) in many areas of proficiency.
UrbanDicionary.com - In their own words "A website with a brilliant concept that could have become great if it hadn't been overrun by a mob of losers, who spend their days trying to feel important and popular by insulting everything else on God's green earth."
Not true at all.
Actually Ubuntu means (from the site):
Ubuntu is an ancient African word meaning 'humanity to others'. It also means 'I am what I am because of who we all are'. The Ubuntu operating system brings the spirit of Ubuntu to the world of computers.
And also from ubuntu site:
Debian is 'the rock upon which Ubuntu is built'.
So, Ubuntu is a Linux Distribuition derived from Debian.
Urban Dictionary isn't really a source for correct definitions - while "humorous", that's not really what it means.
What Ubuntu means has been well covered here: What does "Ubuntu" mean? - Ubuntu was once considered a flavor of Debian and that's where it's roots are. Debian, in my opinion - back when Ubuntu came about - was more of a start towards desktop Linux and still had it's roots very much in Servers.
Ubuntu project took what Debian had going for it (Package Management, Philosophy, etc) and spearheaded on the "Linux for Humans" and not for servers campaign, and here we are today.
The term Ubuntu has been explained in this question What does “Ubuntu” mean?
Yes. Ubuntu is based on Debian. The packages used are to a high extend identical. Ubuntu has in contrast to Debian a regular release schedule, and is more focused on stability and the needs of end users. Debian has more freedom for experimental packages and is a very good distribution for developers.
Thought I would throw in this short clip of Nelson Mandela's definition of Ubuntu.