means The process by which a group, opinion, or physical phenomenon divides into two sharply opposed extremes with little remaining in the middle.

from From 'polar,' which comes via Latin from Greek 'polos,' the pivot or axis around which the heavens turn — the same root that gives us the North and South Poles. 'Polarization' began as a scientific word in optics and electricity, describing light or charges being forced toward opposite orientations; the figurative sense of people splitting into hostile opposites is a later borrowing of that physics into politics.