Year 204 (CCIV) was a leap year starting on Sunday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Cilo and Flavius (or, less frequently, year 957 Ab urbe condita). The denomination 204 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.

The .204 Ruger is a centerfire rifle cartridge developed by Hornady and Ruger. At the time of its introduction in 2004, the .204 Ruger was the highest velocity commercially produced ammunition, and the only cartridge produced commercially for bullets of .204 inch/5 mm caliber.