Game concept
Stress Level
The game also links it as Stressed, Stress Levels.
From the game's encyclopedia
Every 100 Stress a character accumulates also causes them to gain a Stress Level. Stress Levels range from 0 to 3, with each level imposing increasing penalties to a character's Fertility and Health.
In addition, as long as a character has at least 1 Stress Level, they are vulnerable to Mental Breaks.
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.
Stress Level is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Every 100 Stress a character accumulates also causes them to gain a Stress Level." The game also links it as Stressed and Stress Levels. 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.