What is "dress uniform"

n. a military uniform worn on formal occasions

Dress uniform (often referred to as Full Dress Uniform, to distinguish it from Mess Dress, and from semi-formal uniforms, such as the British Army's Service Dress), is the most formal military uniform, typically worn at ceremonies, official receptions, and other special occasions; with order insignias and full size medals. The dress uniform correspond to the civilian white tie dress code. Uniform design may be distinct to a service (Marines, Army, Navy, Air Force, etc.), or to a Regiment or Branch of Service. Although they are often brightly colored, and adorned with ornaments (gold braid, lanyards, lampasses, etc.), most originated as practical uniforms that, with the adoption of even more practical uniforms, have been relegated to ceremonial functions.

Although many services use the term dress generically for uniforms, allowing it to refer to more modern combat uniforms, with suitable modifiers e.g., the British Army's obsolete Battle Dress (BD), and the US Army's obsolete Battle Dress Uniform (BDU), the term Dress Uniform, without a prefixed modifier, is always assumed to refer to the full, ceremonial dress.