Minimally invasive surgery is a type of surgery reducing the surgical slits to reduce trauma to the body. This surgery is typically implemented using thin-needles and an endoscope to visually guide the surgery.
The main goal of minimally invasive surgery is to lessen postoperative pain and blood loss, lessen scarring and for faster recovery. For example, several minimally invasive spine fusion surgery devices have been intended with the objective of letting placement of pedicle screws and rods into the spine using several smaller openings rather than the one longer cut used in open spinal fusion surgery. The theory is that the screws and rods are positioned into the spine with minimal trauma to the muscle and tendons in the back.
You can also check the overview of Minimally invasive surgery also known as MIS at http://sdspineinstitute.com/minimally-invasive-surgery.html