Loran is a terrestrial radio navigation system that was developed during World War II. It uses a network of ground-based radio transmitters to provide accurate positioning information to ships and aircraft. By measuring the time it takes for radio signals to travel from multiple transmitters to a receiver, Loran can determine the receiver's location with a high degree of precision. The system has evolved over the years, with various versions such as Loran-C and eLoran. Although it has largely been replaced by satellite-based systems like GPS, Loran remains a reliable backup for navigation in areas where satellite signals may be weak or unavailable.