Literally: not – lean – not – faction
Alternately: Impartial. Unbiased. Neutral. Independent. Moved by facts, reason, and what is right and true rather than partisan bickering or blind loyalties.
Notes: This compound comes from a text called the Mozi (墨子) and describes one of the ideals of Mohism, a largely-lost ancient Chinese philosophical movement that (to a degree) opposed Confucian ideas in favor of self-aware reflection and impartial, universal love for humanity.
It’s also one of many yojijukugo of the pattern 不〇不●, which I find interesting for no clear reason.