Any technique used when playing mallet percussion, especially the marimba, which is both the most common tonal percussion instrument, and the one on which four-mallet technique is most likley to be used. Mallet technique can include anything from the number of mallets in each hand (you can hold up to four, but two to a hand is the most common multiple-mallet technique) to the way you move around the instrument to the way you subdivide your rolls.