Discectomy is surgery to remove lumbar (low back) herniated disc material that is pressing on a nerve root or the spinal cord 
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It tends to be done as microdiscectomy, which uses a special microscope to view the disc and nerves. This larger view allows the surgeon to use a smaller cut (incision). And this causes less damage to surrounding tissue.
Before the disc material is removed, a small piece of bone (the lamina) from the affected vertebra may be removed. This is called a laminotomy or laminectomy. It allows the surgeon to better see the herniated disc .
Source: http://www.webmd.com/back-pain/discectomy-or-microdiscectomy-for-a-herniated-disc