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1.
A musical chord formed by a root note, its fifth, and its octave. Among the easiest types of chords to play on the guitar, due to an easily shiftable fingering position, and the power chord's ability to "fit" over both major and minor melodies. Vital to heavy metal and punk music.
Old Black Sabbath and AC/DC albums have a lot of simple yet great power chord-strumming songs.
by Bill M. September 20, 2004
 
2.
a major chord contains the 1, 3rd, and 5th notes in the major scales. a power chord omits the 3rd, and inludes only the fifth. powerchords often include the 8th, which is really just the 1st, an octave higher.
G5 Powerchord

e|-
b|-
g|-
d|-
a|5
e|3

G5 with the octave

e|-
b|-
g|-
d|5
a|5
e|3
by jason August 04, 2004
 
3.
A musical chord which is not technically a chord since it only contains two pitch classes (making it an interval). It is formed by the root note, 5th and commonly features the octave above the root.

It is used by rock guitarists way too often by stringing different power chords together to form a riff. This goes against western diatonic music theory which says you should not have parallel 5ths or octaves, let alone both of them simultaneously. Despite this fallacy, rock guitarists have chicks and money while classical musicians have neither. Go figure.
That guy looks sad, lonely and poor.

Yeah. He mustn't use power chords.
by HumphreyB May 02, 2006
 
4.
A common 'chord' used mostly in gutiar based music. It is made by playing the root, 5th and 8th.

For the person who said that parallel 5ths and 8ths shouldn't be even used, I think you'll find this is only relevant to Baroque and Classical music. What about Debussy and his use of 5ths and 8ths? In the right context, it can sound fine.

So please, stop living in the 18th century.
I'm going to play a Power Chord by fretting G, D and another G.
by Flealan August 10, 2010