From the game's encyclopedia
An Activity in which a Host invites various Characters to offer their respect after a recent Character Death. Funerals often result in increases in Legitimacy, decreases in Stress, and opportunities to show Piety.
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.
Funeral is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "An Activity in which a Host invites various Characters to offer their respect after a recent Character Death." It is part of Activity. The game also links it as Funerals. Patch 1.20.1.2, from game/common/game_concepts/06_ce1_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/06_ce1_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.