The word 'epidural' simply refers to a layer of supporting tissue outside the spinal cord. In an epidural a solution of long acting local anaesthetic, long acting anti-inflammatory steroid, and sometimes other pain modifying drugs is injected into the epidural space in the spine. The approach is typically intralaminar (ie down the middle) versus a transforaminal technique (from the side, through the nerve root window). These injections are typically done as therapy, but occasionally a diagnostic result is needed. This is called a selective nerve root block (or SNRB). This can help clarify a therapeutic target.