Lumbrosacral refers to the lower part of the spine where the lumbar vertebrae meet the sacrum. Radicular in this context is a term to describe nerve pain that travels from the low back down the leg.
Syndrome lets you know that there are two or more symptoms commonly associated with this condition. A simpler, more familiar term for lumbrosacral radicular syndrome (LRS) is sciatica.
Tension or pressure on the nerve root is the most common cause of sciatica or LRS. Disc problems, tumors, and stenosis (narrowing of the spinal canal) are the most likely sources of nerve impingement causing sciatica.