Saturnalia (from the god
Saturn) was the name the
Romans gave to their holiday marking the
Winter Solstice. Over the years, it expanded to a whole week, the 17th thru 23rd of December. It also degenerated from mostly tomfoolery, marked chiefly by having masters and servants switch places, to sometimes debauchery, so that the (lower case) word "saturnalia" came to mean "orgy."
The customary greeting for the occasion is, "Io, Saturnalia!" -- io (pronounced "yo") being a Latin interjection related to "ho" (as in "Ho, there").
Other Roman festivals and rites include the Ambarvalia and the Lupercalia.