Perforator flap concept plays an important role in reconstructive surgery, because it allows less invasive and more complex reconstruction by preserving major vessels and muscles with intramuscular vessel dissection. Originally "perforator" represents vessel perforating the muscle, then vessel perforating the deep fascia regardless of muscle perforation. With technical progress in reconstructive microsurgery, the previous definition becomes inappropriate for least invasive flaps, only requiring intra-adiposal vessel dissection, such as superficial circumflex iliac artery perforator flap. Based on our experience of various least invasive flap reconstructive surgeries, a new concept for perforator flap has been developed. The new definition of perforator is a vessel perforating an envelope of a targeted tissue to be transferred; the superficial fascia for skin, the periosteum for bone, the perineurium for nerve, and the deep fascia for muscle. According to the new definition, all flaps can be precisely classified based on the corresponding "perforator".