An "epidural" involves the placement of a small catheter into the epidural space to run a dilute local anesthetic infusion with or without a narcotic. They are used to treat post-operative pain after major abdominal or thoracic surgery. They are also used to provide analgesia for labor. In some cases of low back pain and sciatica, an epidural steroid injection will be administered to treat the pain.
In layman's terms, the spinal cord is surrounded by a tissue sack. The epidural space is just outside this tissue sack. An anesthesiologist will use a special technique with a special needle and syringe to place the tip of the needle between the bones of your back into this space. While a single dose of medication can be administered and the needle removed (such as the epidural steroid injection), usually for labor or post-op pain, a catheter (small plastic tube) is inserted through the needle before the needle is removed. The medication is administered through this catheter to treat pain or provide labor analgesia.
The difference between an epidural and a spinal is, an epidural stays outside the tissue sack, the spinal pierces it.
I have had an epidural after major abdominal surgery and it helped cut down the amount of pain medicine I needed. I was able to walk around even though my stomach was partially numb.