When used with respect to survey ["control"], order is a specification of the accuracy and precision of the measurements that were made. The ["NGS"] has standards that must be met for the different orders of accuracy.
On an NGS datasheet, one of the lines will say "HORZ ORDER" (geocaching datasheets do not have this specification line). The levels of order and their accuracy are:
A - a relative accuracy of 5 mm +/- 1:10,000,000 relative to other A-order stations.
B - a relative accuracy of 8 mm +/- 1: 1,000,000 relative to other A- and B-order stations.