Power Chords Part 1
A chord is three or more different notes played together,. That's usually the one, a third of some kind (major or minor) and a perfect fifth. This combination of three notes is generally too messy and dense to play with very much distortion. During the rock era, the chord was simplified to exclude the third. This saves a lot of hassle with whether the chord is major or minor, or borrowed from a parallel key.
This simple shape is incredibly powerful because it allows anyone to write a song they can play on acranked up amp. However, after fifty years or so, the same truncated chord voicings can become boring.
New Definition: A power chord is any two notes that paraphrase a larger chord.
Here is a power chord primer to give you some new ideas for loud rhythm playing the chords follow a general progression of complexity.
The most familiar shape of a power chord is a note and the fifth above it.
To this we add the octave.
If we remobe the original note and play only the fifth and root in the higher octave, we get the third most common voicing, used moke recognizably in "Smoke on the Water." This interval is the perfect fourth, the inversion of a perfect fifth.
Metal bands sometimes use a "double fifth" voicing to add extra lows and dissonance to a power chord with a root on the A string.