It really takes 365.242190 for the earth to make a trip around the sun.
(The mean time between two successive vernal equinoxes is called a tropical year, or a solar year)

So, to keep it all balanced out,  every 4 years, an extra day is added to February in the Gregarian calendar. In America, those years also coincide with presidental election years.

In the English speaking a world, it is a tradition that women may propose marriage on leap years. For men and woman alike, Hawaii is a romantic place to pop the question, tie the knot or enjoy the honeymoon or anniversary all 365.242190 days a year!

A leap year is a year in which an extra day is added to the calendar in order to synchronize it with the seasons.

Since the tropical year is 365.242190 days long, a leap year must be added roughly once every four years (four times the fractional day gives ). In a leap year, the extra day (known as a leap day) is added at the end of February, giving it 29 instead of the usual 28 days.

In the Gregorian calendar currently in use worldwide (except perhaps the Russian and Iranian calendars), there is a leap year every year divisible by four except for years which are both divisible by 100 and not divisible by 400. Therefore, the year 2000 will be a leap year, but the years 1700, 1800, and 1900 were not.

When Great Britain (and America), adopted the Gregorian calendar in September 1752; 11 days were dropped.

In traditional cultures, it was customary to have lunar (moon) calendars, with 12 and/or 13 months every year. To align the calendar with the seasons, the 13th month was inserted as a "leap month" every two or three years. Many countries, especially in Asia still use such calendars.

The Gregorian calendar was designed to keep the Vernal Equinox on or close to March 21, so that the date of Easter (celebrated on the Sunday after the 14th day of the Moon that falls on or after 21 March) remains correct with respect to the vernal equinox. The Vernal Equinox year is about 365.242374 days long (and increasing), whereas the average year length of the Gregorian calendar is 365.2425.

The Chinese calendar is lunisolar, like the Hebrew calendar, so a leap year has an extra month, often called an embolismic month after the Greek word for it.

In the Chinese calendar the leap month is added according to a complicated rule, which ensures that month 11 is always the month that contains the northern winter solstice. The intercalary month takes the same number as the preceding month; for example, if it follows the second month (二月) then it is simply called "leap second month" (traditional Chinese: 閏二月; simplified Chinese: 闰二月; pinyin: rùn'èryuè).

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