Impeach can mean the process in the US Constitution where the House of Representatives votes to accuse a government official (such as the President or a federal judge) of misconduct. The Senate is responsible for trying the official after they are impeached in the House.
To impeach may also refer to the process in a trial where one party attempts to discredit the credibility of a witness. For example, a witness who claims to have seen a crime occur could be impeached with evidence that the witness was actually in another city when the crime occurred and could not possibly have seen what they claim to have seen.
