Game concept
Religious Family
The game also links it as Religious Families.
From the game's encyclopedia
A Religious Family is a group of Religions. The Religious Family affects how the various Religions, and Faiths therein, view each other.
The Abrahamic Family condones Holy Wars against everyone (including other Abrahamics). Religions are susceptible to Heresy.
The Dharmic Family only condones Holy Wars against other Religious Families.
The Pagan Family condones Holy Wars against everyone, but Faiths within the Religions must be reformed to access them.
The game's text for patch 1.20.1.2. Words in blue are entries of the encyclopedia: hover one to read it, as in the game.
Religious Family is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "A Religious Family is a group of Religions." The game also links it as Religious Families. Patch 1.20.1.2, from game/common/game_concepts/00_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/00_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.