Game concept
Breeding
The game also links it as Bred, Breed.
From the game's encyclopedia
By arranging Marriages between characters with good Congenital Traits, it is possible to breed children with the same Traits. Lucky offspring might even get a reinforced version of such Traits.
However, the same is true of bad Congenital Traits like Ugly.
It might be tempting to arrange marriages between closely related characters in order to produce better Traits in your children, but this also carries the risk of Inbreeding defects.
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.
Breeding is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "By arranging Marriages between characters with good Congenital Traits, it is possible to breed children with the same Traits." The game also links it as Bred and Breed. 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.