While this doesn't always refer to a "true" pedal-point as defined by classical music, the technique sharing the same name in metal describes a riff consisting of a melody line punctuated by a single repeating note, usually an open note on the lowest string.
This technique's main purpose is to elongate a riff, enabling it to cover a greater span of time without adding in too many additional notes or changing the rhythm. One could argue that the same could be achieved by simply palm-muting the most recently-played note in the riff, but this negates the unique sort of "bouncy" feeling that pedal-point riffing provides.
For demonstrated applications of this technique, as well as an example from a full original song, have a look at the following video:
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