Hair transplantation is a surgical technique that involves moving skin containing hair follicles from one part of the body (the donor site) to bald or balding parts (the recipient site). It is primarily used to treat male pattern baldness, whereby grafts containing hair follicles that are genetically resistant to balding are transplanted to bald scalp. However, it is also used to restore eye lashes, eye brows, beard hair, and to fill in scars caused by accidents and surgery such as face lifts and previous hair transplants. Hair transplantation differs from skin grafting in that grafts contain almost all of the epidermis and dermis surrounding the hair follicle, and many tiny grafts are transplanted rather than a single strip of skin.

Since hair naturally grows in follicles that contain groupings of 1 to 4 hairs, today’s most advanced techniques transplant these naturally occurring 1 – 4 hair "follicular units" in their natural groupings. Thus modern hair transplantation can achieve a natural appearance by mimicking nature hair for hair. This recent hair transplant procedure is called "Follicular Unit Transplantation."

From http://en.wikipedia.org/wiki/Hair_transplantation