°In the Gregorian calendar, a year having 366 days instead of the usual 365, with the extra day added to compensate for the fact that the Earthrotates approximately 365.25 times for each revolution it makes around the Sun.
°In the Jewish calendar or other lunisolar calendars, a year having 13 months instead of 12, with the extra month added because 19 solar years is approximately 19*12+7 lunar months.