This is a form of soft tissue mobilization, where instead of taking multiple sessions of massage to reduce a trigger point, with a small filiform needle, it can be significantly reduced, if not eliminated.
Dry needling is an advanced skill that can be performed by a physical therapist. It is not acupuncture, as it is not purposely treating energy or acupuncture meridians, but rather a trigger point in a muscle.
Trigger points are taut bands in a muscle that are undergoing a state of constant contraction. This stagnant state can cause local as well as referred pain, and by and using dry needling to eliminate this trigger point, rapid improvement is typically found.
See Noelle Dowma DPT's dry needling educational background.