Leap Years come once every 4 years. There are 366 days in the year instead of the usual 365. The extra day is added on in February, the shortest calendar month. Instead of 28 days in the month, there are 29.
Leap DAY, February 29th, comes only once every 4 years, so it is not a very common day at all. I thought it would be fun do have a group about Leap Day.
See the kinds of wallpapers that fit into this group; they are listed in the group details.