formal ceremony to mark the beginning of a major public leader's term of office, or official opening or beginning of an institution or structure

Inauguration is a ceremony marking the beginning of a politician taking office or the opening of, for example, a bridge.

Inauguration of the railway bridge over the Daugava river in Riga, Latvia in 1914

When a politician, for example a President, takes office, he may make an oath of office in front of an audience as part of the inauguration ceremony.

The Inauguration of the President of the United States takes place on January 20 in the year after an election.