A person who was born on the 29th of February. So if they were born on the 29/02/2004 they will only be 2 years old now (2012) because it is only the 2nd time it is the 29th of February. They are actually 8 but it only the 2nd time that it is the actual date of their birthday.
Friend: Happy 8th birthday!
Birthday person: Thanks.
Other friend: No he's only 2.
Other friend: because its only the 2nd time it is the 29th of February! He's a leapling!
Friend: That's true!
Both friends: Happy 2nd birthday!