What does "D'ou" mean? And why is it not explained?

Bonjour Bo,

"D'où" is the contraction of "de + où" (from + where). De becomes d' because it's followed by a vowel (Où).
This lesson is more about understanding this question, but mostly about answering it for yourself.
However, we've decided to add a comment to our lesson to clarify this point :)

A bientôt !

Hi Bo, it's a contraction of "de + où" and literally means "from where". "Tu viens d'où" = "You come from where?" (Where are you from?"