Sachin Kanaujia is correct. They are used in geoprocessing to fully store or create a spatial reference, but a regular 'prj' or coordinate system string doesn't include these values. They are, in order:
minimum x value
minimum y value
xy precision (1/precision = xy resolution)
minimum z value
minimum measure value
IsHighPrecision: marker that the spatial reference is high precision, rather than the older standard precision.