What is "shoulder sleeve insignia"

A shoulder sleeve insignia (often abbreviated SSI), is an embroidered patch used by major formations of the United States Army. Each formation has a unique formation patch, and the U.S. Army is unique among the U.S. Armed Forces in that all soldiers are required to wear the patch of their headquarters as part of their military uniforms.

Shoulder sleeve insignia receive their name from the fact that they are most commonly worn on the upper left shoulders of all U.S. Army uniforms, though they can be placed on other locations, notably a combat helmet. Shoulder sleeve insignia worn on the upper right shoulders on Army uniforms denote former wartime service. These "combat patches" will not be worn on the new Army Service Uniform. Instead a 2 inch metal replica will be worn on the right breast pocket and is officially known as the Combat Service Identification Badge.