(n.) A year where Febuary has 29 days. This is because the earth actually takes 365.24 days to orbit the sun completely. This figure is rounded to 365.25, so after four years, we have to add an extra day. However, since it is actually a little less than a whole day, every 100 years we will be a day ahead. There are 10 leap years in 100 years, and hence, we must miss one of these years. This was last done in 1900, and shall next be done in 2100, hence, it is unlikely many of us will live to see the next one, unless this definitions is still here (along with urbandictionary of course!) in many years' time.
1) Every year divisible by four is a leap year (1996,2000, 2004);
2) Unless it is also divisible by 100 (1700, 1800, 1900, 2100).
3) However, if a year is divisible by 4, 100 and 400, it is a leap year (1600, 2000, 2400)