Any book written by an author born in a leap year. The author does not have to be born in February and the book does not have to have been published in a leap year.

Examples of leap years: 1904, 1908, 1912, 1916, 1920, 1924, 1928, 1932, 1936, 1940, 1944, 1948, 1952, 1956, 1960, 1964, 1968, 1972, 1976, 1980, 1984, 1988, 1992, 1996, 2000, 2004, etc.