X-ray impression: levoscoliosis versus positional curve centered at the t4 level & reduction in disc space height at l5-s1 what does that mean?

It means the image could be explained by a transient process causing pain (muscle spasm) or it could be a mild longstanding tilt of the spine to the left at T4. Reduction in disc space just means the pads between the vertebral bones are flattened. The meaning in this case should be interpreted by the doc who ordered the study & knows the case.