Game concept
Mercenary Contract
The game also links it as Mercenary Contracts, Mercenary Contract's, Mercenary Contracts'.
From the game's encyclopedia
A Mercenary Contract involves aiding a Character in either an on-going War, or else one they intend to start with your help. Pay is awarded based on War Contribution, as well as the actual result.
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.
Mercenary Contract is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "A Mercenary Contract involves aiding a Character in either an on-going War, or else one they intend to start with your help." It is part of task_contracts. The game also links it as Mercenary Contracts, Mercenary Contract's and Mercenary Contracts'. Patch 1.20.1.2, from game/common/game_concepts/07_ep3_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/07_ep3_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.