What do you call the main section of a song that usually introduces new ideas?

Lyrically, "the verse contains the details of the song: the story, the events, images and emotions that the writer wishes to express....Each verse will have different lyrics from the others." A verse exists primarily to support the chorus or refrain...both musically and lyrically." A verse of a song, is a repeated sung melody where the words change from use to use (though not necessarily a great deal).

Musically, "the verse is to be understood as a unit that prolongs the tonic....The musical structure of the verse nearly always recurs at least once with a different set of lyrics." The tonic or "home key" chord of a song can be prolonged in a number of ways.