(covers information from several alternate timelines)
Favoritism or playing favorites was preferential treatment given to a certain individual based on one's admiration of or relation to the same, rather than individual merit.
Tom Paris received a B minus in his Survival Strategies course at Starfleet Academy. When he related this to Neelix in 2372, adding that his father was teaching the course at the time, the Talaxian was surprised, commenting that the elder Paris didn't play favorites. (VOY: "Parturition")