Many pop songs destined for radio airplay feature both an instrumental introduction and an instrumental fadeout, known in the entertainment business as an intro and an outro. A well-produced outro gives the song a satisfying conclusion so the next song's intro is not jarring to the listener. Sometimes a song, particularly a classical piece or vintage standard, will feature a definitive tag or extro instead of simply fading out. The "shave and a haircut" ending to barbershop quartet music would be considered a tag or outro, for example.
The outro of a pop song allows the disk jockey enough time to announce the name of the song or artist, identify the station and/or introduce the next song with an underlying sound bed. Some songs, such as the Eagles' "Hotel California" feature very long outros with extended guitar solos and a gradual fade. Other songs, such as the Romantics' "What I Like About You," end more abruptly, an effect known as a cold outro. Songs with cold intros and outros may require the disk jockey to fill in the gap with on-air patter or a pre-recorded musical jingle.
An outro generally follows the final chorus of a pop song, and may or may not retain the opening structure of the song itself. The extended outro of Lynyrd Skynyrd's anthem "Freebird" is more of a twin lead guitar jam played in a faster tempo than the gospel-tinged verses and choruses. The outro to Cream's magnum opus "Badge" features a piano-and-guitar duel which repeats and expands on the piano riff heard throughout the song.
Other outros are created during the editing phase, not the performance phase. The outro to the Beatles "Hey Jude" is a gradual fade-out of the band and others repeating the simple but effective "nah nah nah, NAH NAH NAH NAH" chorus while Paul McCartney drives the song with ad libbed shouts and shrieks. Because the performers were in such a groove, the song itself could have continued until everyone collapsed from exhaustion. Instead, the engineers created a more radio-friendly outro by fading the song out at its peak.
Not all songs have or even need extended outros, but many songwriters understand the needs of the broadcast industry and make efforts to provide a satisfying conclusion which would segue more or less seamlessly into the next song on the radio or at a dance party.