A four-leaf clover is a rare variation of the common three-leaf clover, or white clover (Trifolium repens). Each leaf is said to represent something special: hope, faith, love, and luck. Finding one is considered a good omen, as they are estimated to occur in about 1 in 5,000 clovers. The belief in the luck of four-leaf clovers dates back to ancient times, with Celtic traditions associating them with protection against evil spirits. Today, they are often sought after as symbols of good fortune, especially during St. Patrick's Day celebrations.