The easiest way to explain an array of file names is to show an example.
Say, we want to defined the array "COS$". And we want that array to have 7 elements.
We pick a spot in the list of registers where 7 consecutive registers are available.
R0105 COS$ 0.00 SUNDAY.LOG R0106 0.00 MONDAY.LOG R0107 0.00 TUESDAY.LOG R0108 0.00 WEDNESDAY.LOG R0109 0.00 THURSDAY.LOG R0110 0.00 FRIDAY.LOG R0111 0.00 SATURDAY.LOG
The system that uses this array of file names (the change of state logger in this case), will use the file SUNDAY.LOG if COS$=0, MONDAY.LOG if COS$=1, and so on.