Meaning if line 1 is busy it will roll over to line 2 an on down to your last line. Do not put the fax line in the hunt group, because if all lines are busy the next caller will get the fax machine.
When ordering your CO lines from your local telephone company order them in a hunt group, i.e. order 6 lines, put 5 in the hunt group and designate 1 line for the fax machine.