The indie rock shuffle consists of the rhythmic moving of the torso and head back and forth while performing on a guitar/bass, leaning over the instrument (which is usually worn fairly high), at an awkward angle.
It isn't technically a shuffle, because oftentimes the musician isn't moving their feet at all.
The name is derived from the fact that it has become custom for indie
guitarists and bassists to unconsciously move like this while performing.
Somtimes mistaken for a standing seizure, it's the indie guitarist's substitute for headbanging.