A uniform is a set of standard clothing worn by members of an organization whilst participating in that organization's activity.
People performing religious activities have often worn standard costumes since the dawn of recorded history. Other early examples of uniforms include the clothing of the armies of the Roman Empire and other civilizations.
Modern uniforms are worn by armed forces and other paramilitary organisations such as police, emergency services, security guards, in some workplaces and schools, and by inmates in prisons.
One purpose of military uniforms is to clearly distinguish combatants who are protected by the laws of war from other persons carrying weapons, who enjoy no such protection. Another purpose in historical times was to make it difficult for deserters to avoid detection; military uniforms were so distinctive with many metal buttons and unique colors that they could not be modified into unrecognizable clothing.
Originally, the typical colour scheme included bright and high contrast colour arrangements which made the uniforms visible in battles with much smoke from gunpowder. However, with the growing prevalence of accurate rifles and other ranged firearms as standard weapons for infantry, it was found in the Crimean War that these colours made soldiers easy targets for enemies to shoot at a distance. In reaction, the various militaries, beginning with the British, changed the colours, predominantly to such ones that blended in more with the terrain (like khaki) for the purposes of camouflage. In addition, this idea was followed with uniforms suitable for particular climates and seasons such as white for snowy regions and tan for sandy ones.
Prison uniforms often consist of a distinctive orange or yellow jumpsuit or a white and black zebra striped uniform to make escape more difficult.