“Denazified, that is, destroyed.” What is denazification and how is it understood in Russia?

Since the Russian invasion of Ukraine began, the government and state media have frequently used the word “denazification.” At the beginning of June, we once again heard it in connection with the news from occupied Kherson: a video appeared on the Internet where residents of the region apologize to the Russian army and say that they have undergone a “denazification course.” Despite its frequent use, not everyone still understands what exactly this word means.