Calendar
From Memory Alpha, the free Star Trek reference.
A calendar can be any system of measuring long periods of time, including days, months and years.
In Human standards, a calendar is usually a visual chart representing "months."
In 2376, Neelix proposed a riddle to Tuvok while the two were on an away mission: an ensign was stranded on an uninhabited moon, without food, and all he had was a calendar. How could he survive? Eventually, Tuvok came to the "illogical" conclusion that the ensign could survive by eating the "Sundays." (VOY: "Riddles")
