The word "lumbar" is related to the lower part of the back, specifically the area between the ribs and the pelvis. It is commonly used to refer to the five vertebrae in this region of the spine. "Loin" on the other hand, refers to the area on either side of the spine between the lower ribs and the pelvis, typically associated with meat cuts. Therefore, "lumbar" is the correct answer as it is directly related to the lower back region.