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.