What are holy days for Witches?
Depends on the witch. Some hail to 8 holy days, some 4, me? Moon phases, Halloween (Samhain) and the equinox/solstices. My least favorite solstice is the Summer solstice because I deplore summer but then again, I do live in Southeast Texas so . . .
Some spells/rites are geared to a specific time of the year or a particular phase of the moon. Some study can give you a background on this. I'll talk a little about books next entry.