The process or act of repolarizing; the restoration of a polarized condition
In physiology, repolarization is the process or act of restoring the polarized condition across the plasma membrane of a cell, e.g. nerve cell. During the normal resting state, the membrane potential is a negative value. But the negative membrane potential changes to positive following the depolarization of an action potential. However, this shift from negative to positive value is only for a brief moment in time. The membrane potential returns to the resting membrane potential (which is negative value). The process or act of returning to a negative membrane potential is repolarization.
Repolarization occurs through the physiological mechanisms involving K+ channels, such as A-type channels, delayed rectifiers, and Ca2+-activated K+ channels.1 One such mechanism is when there is an efflux of K+ ions from the cell via the K+ channels in the plasma membrane. In general, the process of repolarization takes several milliseconds. 2
Word origin: re- (again) + polarization
1 Purves D, Augustine GJ, Fitzpatrick D, et al., ed. (2001). Neuroscience (2. ed.). Sunderland, Mass: Sinauer Assoc.
2 Jeff Hardin; Gregory Paul Bertoni; Lewis J. Kleinsmith. Becker's World of the Cell. Benjamin-Cummings Publishing Company; December 2010. p. 389.