Security officer
A security officer or security guard was an officer whose duties were to provide security or perform guard detail. The head security officer was generally known as the chief of security.

In 2366, Captain Jean-Luc Picard received a message from the security officer of the Klingon warship . ()

The Rakhari Croden told Constable Odo, with fear and hate, about the Rakhari security officers who came in his home at night and killed his wives. When Odo and Croden later unlocked Croden's daughter Yareth from a stasis pod on an asteroid in the Chamra Vortex, Yareth looked with fear at Odo until her father explained that the security officer was a good one. ()

Starfleet 
Starfleet Security officers were part of a starship or starbase's security department, under the command of a chief security officer. 

A complete study of starship security protocols was generally considered a requirement to fully qualify one to serve in the capacity of a Starfleet security officer. () 

A security officer's duties included the protection of Starfleet and Federation assets, the prevention and investigation of crimes, and personal protection of Starfleet officers and Federation or foreign dignitaries.

During the 23rd century, it was customary for landing parties to include a number of security officers as guards.

List of noted security officers 
 Pavel Chekov (Starfleet)
 Davison (Starfleet)
 Dickerson (Starfleet)
 Michael Eddington (Starfleet)
 David Garrovick (Starfleet)
 Garvey (Starfleet)
  (Starfleet)
 Ty Kajada (Kobliad Security)
 Kellogg (Starfleet)
  (Markridge Industrial Tower)
 Kurn (Bajoran Militia)
 Lipton (McKinley Rocket Base)
 Neelix (Starfleet; alternate timeline)
 Odo (Bajoran Militia)
 Christopher Pike (Starfleet)
 George Primmin (Starfleet Security)
 Malcolm Reed (Starfleet)
 Sandra Rhodes (Starfleet)
 Seelee (Bajoran Militia)
 Sito Jaxa (Starfleet)
 Thrax (Cardassian Union)
 Tuvok (Starfleet)
 Worf (Starfleet)
 Natasha Yar (Starfleet)

External link
 

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Titles
Legal occupations