Kostadin is a common male given name in several Slavic countries, including Bulgaria, Serbia, and North Macedonia. The name is derived from the Greek name "Konstantinos," which means "constant" or "steadfast." It is often associated with individuals who are reliable and strong in character. In Bulgaria, Kostadin is celebrated on St. Constantine and Helena Day, which falls on May 21. This day honors the legacy of Constantine the Great, the first Roman emperor to convert to Christianity. Many people named Kostadin may celebrate their name day on this occasion, reflecting cultural traditions surrounding names and their significance.