Red Shirt

Red Shirt is a nickname of Starfleet's security personnel, named for the distinctive red shirts they wore in the original Star Trek series. Red Shirts are notable for their high casualty rate, as Red Shirts who accompany senior officers of the ship on missions frequently die. The name was retained even after security switched to yellow shirts in the post-TOS series.

Although their job description suggests that their role should be limited to providing security on starships, Red Shirts seem to the only foot soldiers available to the Federation, performing the roles of army and marines in addition to shipboard security.