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.

किसी संस्था के सदस्यों द्वारा, संस्था का कार्य करते समय, पहना जाने वाला मानक वस्त्र वर्दी' कहलाता है। आधुनिक समय में सेना के अधिकारी और सैनिक, अर्ध-सैनिक बल पुलिस, विद्यार्थी, वकील आदि वर्दी पहनते हैं।