Gneiss is one of the important type of rocks. If we have to define Gneiss in general, Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks. Gneiss comes under Metamorphic Rocks. All Metamorphic Rocks have similar properties and formation process. Along with Gneiss Definition, know more about the History of Gneiss, Etymology of Gneiss in next sections.