What is mean by miller indices?

Miller indices are a notation system in crystallography used to describe the orientation of crystal planes and directions in a crystal lattice. They are represented as a set of three integers (h, k, l) that are derived from the intercepts of the plane with the crystal axes, inversely proportional to those intercepts. Miller indices provide a concise way to identify and categorize different planes and directions within a crystal structure, essential for understanding its properties and behaviors.