partiality
Unfair favoritism toward one person or group over others.
Partiality means favoring one person, group, or option over others, often in an unfair way. When a teacher shows partiality toward certain students by always calling on them first or giving them easier assignments, the other students notice and feel the unfairness. When a referee displays partiality by making calls that favor one team, the game stops being fair.
The word comes from being partial to something, which means liking it more than the alternatives. You might be partial to chocolate ice cream over vanilla, which is harmless. But partiality becomes a problem when someone in a position of authority lets their personal preferences interfere with fairness. A judge who shows partiality in court undermines justice. A parent who shows obvious partiality toward one child over another creates family resentment.
The opposite of partiality is impartiality, treating everyone fairly without favoritism. Good umpires, judges, and teachers strive for impartiality, making decisions based on facts and rules rather than personal feelings. When you're chosen to settle a disagreement between friends, they're counting on you to listen fairly to both sides without partiality.