Iridium is a very rare chemical element in the Earth's crust. It was discovered in 1803 by Smithson Tennant from England, and it got its name from the Latin word iris, which means rainbow, because its joints were extremely colored. It is a hard or brittle metal, silver-white in color, which can be heated up to 2300 °C in air. In the periodic table, it is under serial number 77, atomic mass 192,217(3) and is represented by the symbol Ir. It is the most resistant to corrosion of all metals and is destroyed only by molten alkali. This is exactly why the satellite communication system was named Iridium. The system itself is designed to have as many satellites as the chemical element Iridium has electrons. In order to be able to provide complete global coverage, the system consists of 66 satellites located in six orbital planes at a height of about 780 km from the Earth's surface. Iridium is the most complex telecommunications system that has developed and improved so much since its inception and first launch in 1962 that we have almost complete global coverage of the wireless communication network. The Global Maritime Distress and Safety System is a technical, administrative and operational structure for maritime distress and safety communications around the world established by the International Maritime Organization in 1988. This paper presents in detail all terms related to the Iridium satellite and communication system, the types of devices in Iridium system and types of modems and terminals.