Complex sentence: It is a muted chord that marks the off-beats or upbeats, in a rhythm guitar and mandolin technique, chucking, in which the chord is muted by lifting the fretting fingers immediately after strumming, producing a percussive effect.
Split into simpler sentences: It is a muted chord that marks the off-beats or upbeats. As a rhythm guitar and mandolin technique, it is accomplished though chucking, in which the chord is muted by lifting the fretting fingers immediately after strumming, producing a percussive effect.