what is a prelude?why is that the title of the story

In fact, William Wordsworth never titled his work The Prelude and died before seeing it published. His widow endowed the unrelenting self-examination of what it means to become a poet composed in blank verse with its title shortly before publishing the first version in 1850. Each of the various existing versions to which the title The Prelude has been attached were conceived by the poet with the intention of becoming part of a far more ambitious magnum opus titled The Recluse. Alas, Wordsworth never quite got around to completing The Recluse before his death.