Today, February 29, is Leap Day, the extra day added to the calendar every four years, not counting century years that aren't divisible by 400, to compensate for the fact that Earth doesn't revolve around the Sun exactly once every 365 days. Another name for Leap Day is Bissextus, which comes from the Latin dies bissextus. A leap year was called annus bissextus. Neither term had anything to do with Roman sexual preferences, instead reflecting how the Romans counted their days.
When the Roman calendar was reformed in 46 BC by Julius Caesar's order, each month had three key days: the Kalends, the Nones, and the Ides.* The Kalends were the first day of the month. The Ides were on the 13th of the month, except in March, May, July, and October, when they were on the 15th. The Nones fell 9 days before the Ides, either the 5th or the 7th, depending on month.
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In March, July, October, May, Nones is the 7th, Ides the 15th day.
Unlike today, the Romans counted their days backwards from the next key day, including both the key day and the day being reckoned in the count. Therefore, our February 24th would be "six days before [and including] the Kalends of March". On leap years, the 24th was doubled, with both reckoned as six days before the Kalends of March. To distinguish between the two February 24ths, dies bissextus was added to the second one. Dies bissextus can roughly be translated as "the sixth day doubled", and annus bissextus as "the year with a sixth day doubled".
Later, when dates were reckoned forward from the beginning of the month as they are now, leap days were moved to February 29th, and Bissextus eventually ended up falling by the wayside. ___________________
* The e's in Nones and Ides are pronounced in Latin – "no-nayz" and "ee-dayz".
