A uniform is a variety of costume worn by members of an organization while usually participating in that organization's activity. Modern uniforms are most often worn by armed forces and paramilitary organizations such as police, emergency services, security guards, in some workplaces and schools, and by inmates in prisons. In some countries, some other officials also wear uniforms in their duties; such is the case of the Commissioned Corps of the United States Public Health Service or the French prefects. For some organizations, such as police, it may be illegal for non-members to wear the uniform.

A security guard is a person employed by a government or private party to protect the employing party's assets from a variety of hazards by enforcing preventative measures. Security guards do this by maintaining a high-visibility presence to deter illegal and inappropriate actions, looking for signs of crime or other hazards, taking action to minimize damage, and reporting any incidents to their clients and emergency services, as appropriate.