leap year

Từ điển Oxford Advanced Learner 8th

ˈleap year [leap year leap years] BrE NAmE noun
one year in every four years when February has 29 days instead of 28

Word Origin:
late Middle English: probably derives from the fact that feast days after February in such a year fell two days later than in the previous year, rather than one day later as in other years, and could be said to have “leaped” a day.

Culture:
the calendar
Britain and the US follow the Gregorian calendar, which replaced the Roman Julian calendar in 1752. The year is divided into 12 months, with 30 or 31 days in each month, except February, which has 28 days. An extra day is added to February every fourth year, called a leap year, to keep the calendar in time with the moon. A well-known verse helps people remember how many days there are in each month: Thirty days hath September, April, June and November. All the rest have thirty-one, Excepting February alone, Which hath twenty-eight days clear, and twenty-nine in each leap year.
The calendar year starts on 1 January, ↑New Year's Day. The number of each year (2003, 2004, et c. ) represents the number of years that have passed since the birth of Jesus Christ. The year 2000 marked the end of the second millennium (= a period of 1 000 years) since Christ was born. The years before Christ are described as BC (= before Christ), e.g. 55 BC, or BCE (= before the Common Era). The abbreviations AD (Latin Anno Domini, meaning ‘in the year of the Lord’) or CE (= Common Era) are put before or after the date for the years after Christ’s birth, e.g. AD 44 or 44 AD, but they are not used with years after about 200 AD. Some cultural and religious groups use different calendars: the year 2000 in the Gregorian calendar began during the year 5760 in the Jewish calendar, 1420 in the Islamic calendar and 1921 in the Hindu calendar.
The academic year used by schools and colleges in Britain runs from September to July, with short holidays at ↑Christmas and in the spring and a long summer vacation. In the US the academic year runs from August or September to May or June. Many business companies have a financial year (= a period of accounting) that runs from April to the following March. The tax year in the US is the same as the calendar year but the tax year in Britain begins on 5 April. The reason is that in ↑medieval times the calendar year began on 25 March, not 1 January. When the Gregorian Calendar was introduced, an adjustment was needed and 11 days were removed from September 1752. To avoid being accused of collecting a full year’s taxes in a short year, the government extended the end of the tax year 1752–3 to 4 April.
Many festivals are celebrated during the year. Christmas and Easter are the main Christian festivals. Jews remember Passover and Yom Kippur. Ramadan, a month of fasting, and Eid ul-Fitr are celebrated by Muslims. Diwali, the Hindu festival of light, takes place in October or November, and the Chinese celebrate their new year in January or February. Special occasions such as ↑Bonfire Night in Britain and Thanksgiving in the US are enjoyed by almost everyone.