Impeachment is a way to remove government officers from office in some countries. It happens when the official does not want to leave his or her job. It is like an indictment (something that the prosecutor needs to get before the trial). Someone is impeached when a legislature votes to do that. Later, there is another vote on whether or not to convict, which is like guilty or not. The second vote may be by the same people who did the impeachment, or someone else as in a bicameral legislature. Several different types of office holders may be impeached, but cases against the President or leader of a country attract the most attention typically.
Two well-known heads of state who were impeached and removed from office were Brazilian president Dilma Rousseff in 2016 and South Korean president Park Geun-hye in 2017. President Bill Clinton, along with other former US Presidents, was impeached, but not removed from office. President Richard Nixon resigned from the office of President before the House could impeach him, resulting in him being the only president to resign.