What is a leap year?
A "leap year" comes every four years, when February has 29 days - (l'anno bisestile).
There is a rhyme in English to help you remember the number of days in each month:
Traditionally in Ireland, as 29th February is a "special" day, this is the day when women can propose to men....who cannot refuse. This is basically the plot of the film "Leap Year" which came out 2 years ago and tells the story of a girl who follows her boyfriend on a business trip to Dublin to propose to him.
A "romantic comedy" that was listed by Time as "The Worst Film of 2010"!
"to leap" means "saltare" and a leap is usually a big jump, as in the famous phrase Neil Armstrong pronounced when he stepped on the moon for the first time in history:
"One small step for man - one giant leap for mankind"
(Un piccolo passo per un uomo, un grande passo per l'umanità) Armstrong, July 21, 1969

It is usually good advice to remeber to "look before you leap"!
30 days has September
April, June and November
All the rest have 31
Excepting February alone
It has but 28 days clear
And 29 in each leap year