The Random Map node will randomize the input texture with the selected Noise Function; Perlin, Unsigned Perlin, Cell and Hash (figure 1). The Scale slider will attenuate the result.
Figure 1: The Random Map node used to modify the output from a Marble Texture node
Input Texture - The texture to operate upon. This can be an image texture or a procedural texture.
Input Scale - The scale of the randomization. Higher values cause repeating patterns.
Noise Function - Determines the function used to generate the random values.