[reedalex01]

More info on their relationship with Debian: https://tails.boum.org/contribute/relationship_with_upstream

"For various reasons Tails tries to diverge by the smallest possible amount from its upstream projects, and especially from Debian"

"We try to push our changes upstream when we need to modify software we ship. This often requires us to write code in a generic way, rather than implementing ad-hoc hacks to fit our specific needs: e.g. we often need to make the stuff we need opt-in and add configuration options."

The official term for this is "Debian derivative" rather than "fork."