In a song that is otherwise sung, a section that is not sung but which is played by instruments can be called an instrumental interlude, or, if it occurs at the beginning of the song, before the singer starts to sing, an instrumental introduction. If the instrumental section highlights the skill, musicality, and often the virtuosity of a particular performer (or group of performers), the section may be called a "solo" (e.g., the guitar solo that is a key section of heavy metal music and hard rock songs). If the instruments are percussion instruments, the interlude can be called a percussion interlude or "percussion break". These interludes are a form of break in the song.
In commercial popular music, instrumental tracks are sometimes renderings, remixes of a corresponding release that features vocals, but they may also be compositions originally conceived without vocals. One example of a genre in which both vocal/instrumental and solely instrumental songs are produced is blues. A blues band often uses mostly songs that have lyrics that are sung, but during the band's show, they may also perform instrumental songs which only include electric guitar, harmonica, upright bass/electric bass and drum kit.
The opposite of instrumental music, that is, music for voices alone, without any accompaniment instruments, is a cappella, an Italian phrase that means "in the chapel". In early music, instruments such as trumpet and drums were considered outdoor instruments, and music for inside a chapel typically used quieter instruments, voices, or just voices alone. A capella music exists in both Classical music choir pieces (for choir without any accompanist piano or pipe organ) and in popular music styles such as doo wop groups and Barbershop quartets. For genres in which a non-vocal song or interlude is conceived using computers and software, rather than with acoustic musical instruments or electronic musical instruments, the term instrumental is still used for it.
Some recordings which include brief or non-musical use of the human voice are typically considered instrumentals. Examples include songs with the following:
Songs including actual musical—rhythmic, melodic, and lyrical—vocals might still be categorized as instrumentals if the vocals appear only as a short part of an extended piece (e.g., "Unchained Melody" (Les Baxter), "TSOP (The Sound of Philadelphia)", "Pick Up the Pieces", "The Hustle", "Fly, Robin, Fly", "Get Up and Boogie", "Do It Any Way You Wanna", and "Gonna Fly Now"), though this definition is loose and subjective.