Redshirt was a colloquialism among Starfleet personnel referring to expendable individuals who died in the line of duty. The term was derived from the mid-23rd century Starfleet uniform, which featured bold red shirts for members of Starfleet security. Despite 24th century Starfleet security personnel wearing yellow uniforms the term continued to be used.
- Quark also notes, in comparing the lifespans of various lifeforms, that redshirts "rarely survive beyond the second act break".
The term "redshirt" has spread from its in-joke origin of the quickly killed supporting characters in Star Trek: The Original Series. The term has been used to refer to expendable characters in other fictional works, as well as by creators of those works.
The notion of the "redshirt" is commonly parodied in other science fictions and comedies, and even in Star Trek publications - the Star Trek: The Manga book Kakan ni Shinkou featured two short comic strips by David Reddick titled The Red Shirts which depicted the ironically comical mishaps of two red shirts (though because it was in the manga book they were depicted in black and white).