"Denazification" was an Allied post-WWII policy of removing from German and Austrian society, culture, press, economy, judiciary, and politics any remnants of National Socialism.
As one part of this, the Allies removed from positions of power and influence those who had been NSDAP members or otherwise associated with the NSDAP. The emergence of the Cold War and the need for a German ally led the Western powers to lose some interest in this aspect of the policy, which affected large parts of population and which was hugely unpopular. In 1951, the provisional West German government granted amnesties to lesser alleged offenders and officially ended this part of the policy.
Many other aspects continue, with National Socialism, National Socialist organizations, and various things associated with it (such as the swastika) being outlawed.