Rhythm Guitar, Rhythm Guitar

In some cases, the chord progression is implied with a simplified sequence of two or three notes, sometimes called a "riff", that is repeated throughout the composition. In heavy metal (or just "metal") music, this is typically expanded to more complex sequences comprising a combination of chords, single notes and palm muting. The rhythm guitar part in compositions performed by more technically oriented bands often include riffs employing complex lead guitar techniques. In some genres, especially metal, the audio signal from the rhythm guitar's output is often subsequently heavily distorted by overdriving the guitar's amplifier to create a thicker, "crunchier" sound for the palm-muted rhythms.

Rhythm guitarists may employ an electric acoustic guitar or a humbucker-equipped electric guitar for a richer and fatter output. Also, rhythm guitarists may use strings of a larger gauge than those used by lead guitarists. However, while these may be practices, they are not necessarily the rule and is subject to the style of the song and the preference of the individual guitarist.

In alternative rock and post punk bands, though, where the band is trying to create an ambient soundscape rather than an aggressive Motrhead-style "wall of sound", the rhythm guitarist may use flanging and delay effects to create a shimmering background.

Source: Wikipedia > Rhythm Guitar