It is like an indictment (something that the prosecutor needs to get before a 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 usually attract the most attention.