[Freesurfer] about aseg.stats

Hello: I have run the recon-all command and it finished without errors. The FreeSurfer has generated a stats file $SUBJECTS_DIR/<subjid>/stats/aseg.stats, there are some information in this file as follows that I can't understand well:

ColHeaders Index SegId NVoxels Volume_mm3 StructName normMean normStdDev normMin normMax normRange 1 2 335490 335490.0 Left-Cerebral-White-Matter 109.0668 9.6489 43.0000 183.0000 140.0000

which number corresponding with Volume_mm3? what does normMean normStdDev mean? what does Index SegId mean?

thanks in advance Tim