Wiktionary
n. (context idiomatic English) A chord or combination of notes used in rock music and typically selected to sound good at high volume and high levels of distortion. Power chords make extensive use of intervals such as open fourths and fifths.
Wikipedia
In guitar music, especially electric guitar, a power chord (also fifth chord) is a colloquial name for a chord that consists of the root note and the fifth. Power chords are commonly played on amplified guitars, especially on electric guitar with distortion. Power chords are a key element of many styles of rock and especially heavy metal music.
Usage examples of "power chord".
In other company, Ray might have been able to make a case for the ain't-broke-don't-fix- it ethic of the finely crafted song, or the sheer visceral impact of a well-timed power chord, but on this occasion it would have been like suddenly announcing he was a Jehovah's Witness and trying to flog Simon The Watchtower.
A roar reminiscent of a Disaster Area power chord overwhelmed Ford's cries of disagreement.
On the first power chord, a whole stack of cheap preowned speakers shorts out.
I lit a cigar, cranked the Mercury up into one loud, long power chord, and headed for our naval base.