This is a shader that evaluates a coherent noise function (potentially summed over several octaves, giving fractal noise, sometimes known as a turbulence function). The output is between 0 to 1 (actually [0,1) ), which can be used as input to several other shader nodes to produce various effects. This is useful for creating many real-world patterns (marble, granite, leather, etc.)

Info: This shader outputs a float value and therefore may prove unpredictable when connecting it to something like a gobo filter which requires color values. A workaround is to build an RGB color from the output of the Noise texture using the float_to_rgb shader.