Unplugged Version

We got asked to play on MTV Unplugged
You should've seen it...
We went right out there and refused to play acoustical versions of the electrical songs

That we refused to record in the first place

—Todd Snider, Talking Seattle Grunge Rock Blues

The Unplugged Version is when a musician releases a new version of one of their songs played primarily with acoustic instruments. Acoustic guitars are used most often, but any instrument capable of being playing without amplification is fair game. It is not uncommon for an artist to release an entire album of Unplugged Versions, either as a collection of older songs or a complete rerecording of a previous album with acoustic instrumentation.

When an ensemble does this, the Unplugged Version may include the entire band on acoustic instruments, or it may be A Day in the Limelight for someone in the band (often literally in a spotlight with an acoustic guitar).

Sometimes inverted, where an artist will release the Unplugged Version of a song first, and rerecord it later with everyone plugged in. This is most common with folk-rock acts that "go electric."

Only counts as Unplugged Version if the musician or song isn't already an acoustic act... unless they manage to make it more acoustic. For acts further along on Mohs Scale of Rock and Metal Hardness, this can be a Surprisingly Gentle Song, but soft-rockers are just as likely to ditch their electric guitars from time to time. If an artist does an acoustic version of somebody else's song, that's Cover Version, not this trope.

At least partially named for MTV Unplugged, a TV series in which well-known artists are invited to play an all-acoustic set. Artists on Unplugged will include a Unplugged Version of at least one of their songs (as shown in examples below), but typically also play acoustic Cover Versions of other songs they like.

Examples from MTV Unplugged

Eric Clapton did acoustic versions of both "Layla" and "Tears in Heaven" for his Unplugged set. This version of "Layla" is nearly as well known as the original and in a bit of Adaptation Displacement, he exclusively plays the acoustic version in concert now, due to the sheer difficulty of coordinating the electric version live.
Dashboard Confessional's performance on MTV Unplugged (and indeed, their entire career) is an amusing inversion. Dashboard was originally Chris Carrabba's solo acoustic outing and many of the songs on their Unplugged album, while still acoustic, appeared for the first time played by a full band. Dashboard would later on release several electrified versions of previously acoustic songs
Paul McCartney's Unplugged (The Official Bootleg) album is among the first unplugged albums ever released and was the very first MTV Unplugged performance/album.
Nirvana's performance on MTV Unplugged contains several of these. Pretty much any pop culture TV show featuring Nirvana will feature the clip of Cobain singing "All in all is all we are" from the Unplugged Version of "All Apologies."
- Actually, while the instrumentation IS gentler, because Cobain was so insecure about playing unplugged, he was playing an electrocustic guitar plugged into an amp hidden in the stage. You can even hear mild distortion effects on a few of the songs (the cover of "The Man Who Sold The World").
Subverted on Bruce Springsteen's MTV Unplugged appearance. He first played an Unplugged Version of the unreleased song "Red Headed Woman." Then, he turned to his band, shrugged, and they all plugged in and played an electric set. The album MTV released for the show had the "Un" of "Unplugged" scratched out.
The Corrs did a show for MTV Unplugged and released it as an album and DVD. Despite not being a huge stretch due to having a central set of instruments of a tin whistle, one guitar, a violin and drums, it let them perform more vocal harmonies and put a larger focus on the violin.
Bryan Adams did an MTV Unplugged show in 1997, which was released as an album and DVD; he debuted three songs in this performance, with another being released on CD for the first time in it. His performance mainly emphasised the acoustic guitar, with heavy drum support.

Unplugged Version albums

Against Me! inverted this by releasing an acoustic EP in 2001, several songs from which would eventually be rerecorded with an electric band for their proper debut LP, Reinventing Axl Rose.
Garth Brooks' Double Live version of "Unanswered Prayers" is just him, his guitar, and 50,000 of his closest friends.
The Foo Fighters 5th album In Your Honor was a 2 disc set, one being electric and the other being unplugged. The tour for that originated a live unplugged album, Skin and Bones. They also have several slower songs on their 6th album "Echoes, Silence, Patience, and Grace".
The Cure's Acoustic Hits was released as a bonus disc on some versions of their Greatest Hits album; it contained newly recorded acoustic versions of all eighteen songs on the North American version of Greatest Hits.
Hella released Acoustics in 2006, an EP consisting of six acoustic versions of previous songs.
In Jars of Clay's Distinct Double Album Furthermore: From the Studio, From the Stage, the "From the Studio" disc consisted of unplugged versions of prior tracks.
Joy Electric's album Unelectric covers his prior Synth Pop songs on acoustic guitar (though they still have some synths, so it's not completely unplugged).
Alanis Morissette released Jagged Little Pill Acoustic, which is the Unplugged Version of her entire debut album.
Tesla: Five Man Acoustical Jam
Los Campesinos' 2010 EP All's Well That Ends consists of acoustic (and slightly re-arranged) versions of a handful of songs from their Romance is Boring album.
Clint Black's D'lectrified was done entirely with acoustic instruments.
The Veronicas have at least two Unplugged EP's in circulation
Erasure: Union Street

Unplugged songs

Bandits Of The Acoustic Revolution is an all-acoustic ensemble founded by ex-members of Catch-22. Most of their material is original, but they did record an version of "Dear Sergio," originally a song from their old band. Two different bands, but the same songwriter.
Dave Matthews Band did an acoustic version of their song "Grave Digger."
George Harrison recorded a well-known acoustic version of "While My Guitar Gently Weeps." It was finally released on The Beatles Anthology.
Daft Punk released an unplugged version of "One More Time," performed by Romanthony (the original singer, without vocoder this time).
Starflyer 59's song "Mr. Martin" started off as an electric guitar-heavy demo on the Ghosts of the Future boxed set, with a softer version on piano and acoustic guitar recorded as a B-side. Then when it came time to re-record the demos for the album Dial M, the band decided they liked the B-side better, so the unplugged version became the official version. And then the next EP featured two more tracks from the album--"The Brightest of the Head" and "I Love You Like the Little Bird"—and a cover version of The Church's "Under the Milky Way", all performed in the same unplugged style.
The Foo Fighters have a solo acoustic version of "Everlong" played by Dave, along with full band acoustic versions of "Floaty", "Everlong", "Next year", "ain't it the life", "Walking after you" (these five were released as b-sides to various singles), "Friend of a Friend", and "Marigold". The last two were both originally penned by Dave Grohl in 1990 and released on a cassette of his songs called the "Pocketwatch demos", and rereleased as full fledged Foo Fighters songs in 2005 on In Your Honor (with "Friend of a friend") and 2006 on their Skin and Bones live cd/dvd (Marigold). Out of all of their acoustic songs, "Everlong" is the best known, and is always played at their concerts, in recent years being played completely unplugged.
Rush released a live acoustic version of their song "Resist" on the live album Rush in Rio. Geddy and Alex perform the song, while Neil takes a break after performing his drum solo.
Weezer have officially released a few acoustic versions as b-sides, namely versions of "No One Else", "Jamie", "Pink Triangle" and "The Good Life" (they've done acoustic versions of other songs which have been bootlegged too): These were all live recordings originally done for radio or TV, and typically feature Rivers Cuomo and Brian Bell playing acoustic guitars, and Matt Sharp singing backup but not playing any instruments - drummer Patrick Wilson would either be totally absent from sessions or would be there to participate in between-song interviews, but not to play.
Even Marilyn Manson have done this - Remix And Repent includes an acoustic version of "The Man That You Fear" subtitled "Acoustic Requiem", and they also did acoustic versions of "Heart-Shaped Glasses" and "Putting Holes In Happiness" as b-sides. Including an acoustic version of "Cake And Sodomy" In the Style Of country on Smells Like Children may or may not count, since no one who is actually in the band performed it (their bus driver Tony F. Wiggins did).
Five Finger Death Punch got in on it too: Some versions of The Way of the Fist include an acoustic version of The Bleeding as an unlisted track.
Kouji Wada performed an acoustic cover of "Hirari", the second themesong of Digimon Savers, for the Digimon Savers Flash Back album in 2008.
Yellow Magic Orchestra's Rydeen 79/07

Examples of Unplugged Version invoked in-work

Newman and Baddiel In Pieces had a series of sketches in which they would pretend to be a techno or synthpop band doing an Unplugged concert. They'd come on, shout the line from the band's big hit, and then shuffle off again in embarassment.
MTV's The State would often lampoon other MTV shows, including Unplugged. One parody was an unplugged version of a song called "You'll Always Give Me A Boner."