"com" and "row" are how the pins are referred to in the ht16k33 chip data sheet. AdaFruit have chosen to call them something slightly different. Not wrong, just different. C0 to C7 are the cathode connections which are called "com0" to "com7" in the data sheet. A0 to A15 are the anode connections which are called "row0" to "row15" in the data sheet.