Skeletal defect in my spine?

Can anyone help explain this a little more? I had an MRI done an my Dr. said I have a skeletal defect in my spine. He said something about discs. I have had a lower back pain for about 3 years, and he says its a skeletal defect, and its not major enough for surgery. Pain is different in everyone, and he said if advil etc don't get rid of the pain I should come back and get cortisone shots. Before I call him back can anyone tell me more about this?