A stardate is a fictional system of time measurement developed for the television and film series Star Trek. In the series, use of this date system is commonly heard at the beginning of a voice-over log entry, such as "Captain's log, stardate 41153.7. Our destination is planet Deneb IV …". While the original method was inspired by the Modified Julian date system currently used by astronomers, writers and producers have selected numbers using different methods over the years, some more arbitrary than others. This makes it impossible to convert all stardates into equivalent calendar dates, especially since stardates were originally intended to avoid specifying exactly when Star Trek takes place.

Star Trek is an American science fiction television series created by Gene Roddenberry that follows the adventures of the starship USS Enterprise (NCC-1701) and its crew. It acquired the retronym of Star Trek: The Original Series (TOS) to distinguish the show within the media franchise that it began.