The phrase "polarity reversal" refers to a situation where something that was previously positive becomes negative, or vice versa. It is a change in direction or orientation of something's characteristics or qualities. Full definition
Sohl, L.E., N. Christie - Blick, and D.V. Kent, 1999: Paleomagnetic polarity reversals in Marinoan (ca. 600 Ma) glacial deposits of Australia: Implications for the duration of low - latitude glaciation in Neoproterozoic time. (pubs.giss.nasa.gov)
And when the suns polarity reversal decreased with speed toward the suns equator, Sunspot activity decreased. (wattsupwiththat.com)
Bogue thinks the quick shift took place near the end of a millennia - long polarity reversal, when a slow magnetic drift accelerated dramatically for reasons unexplained. (discovermagazine.com)