feriae

n. local festival held in honor of a patron saint (in Spain or Spanish speaking countries); week day, any weekday that is not a feast day (Roman Catholic Church)

This article incorporates information from the Catholic Encyclopedia of 1917. A feria (Latin for "free day") was a day on which the people, especially the slaves, were not obliged to work, and on which there were no court sessions. In ancient Rome the feriae publicae, legal holidays, were either stativae (recurring regularly, e.g. the Saturnalia), conceptivae (i.e. movable), or imperativae (i.e. appointed for special occasions).
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Noun
1. a weekday on which no festival or holiday is celebrated; "in the middle ages feria was used with a prefixed ordinal number to designate the day of the week, so `secunda feria' meant Monday, but Sunday and Saturday were always called by their names, Dominicus and Sabbatum, and so feria came to mean an ordinary weekday"
(hypernym) weekday
2. (in Spanish speaking regions) a local festival or fair, usually in honor of some patron saint
(hypernym) celebration, festivity
(classification) Spanish

Days in the ancient roman culture in which all people, including slaves, got a holiday