Impeachment is basically a stage in a process conducted by a legislative body. In this process the legislative body considers whether to forcibly remove a government official from office or not.
Impeachment is when the charges are brought against a government official. The second stage of this legislative process is conviction where it is determined whether to remove the official from office or not.
Impeachment is a legal statement of charges that runs parallel to indictment in criminal law and might not result in removal of the official from the office.