N= dies nefasti. There were 58 per year. No legal action or public voting could take place.
F= dies fasti Legal actions were permitted.
C= dies comitalis. There were 195 per year. On days marked with a C, Romans could meet in assemblies (comitia), but not if the days were on a nundinae
Nundinae= market day, dies fasti
EN= endotercissus = cut, so they were nefasti in the morning and or evening, but fasti in between.
NP signified feriae public holidays.
FP were some sort of religious holiday. We no longer know what the abbreviation means.

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