Impeachment, as defined in Article II, Section 4 of the US Constitution, is a formal procedure whereby Congress brings charges against high-ranking civil servants, such as the president, in an attempt to remove them from office.
Only the US House of Representatives has the power to impeach a federal official, and only the Senate can convict and remove an impeached official.
The House of Representatives impeached only three US presidents - Andrew Johnson, Bill Clinton and Donald Trump - and they were all acquitted by the Senate.