The Cpk Index is a statistical measure used in quality control to assess how well a process can produce output within specified limits. It compares the width of the process variation to the width of the specification limits, indicating how capable a process is of meeting customer requirements. A higher Cpk value signifies a more capable process, while a lower value suggests that the process may need improvement. A Cpk value of 1.0 indicates that the process is producing output that meets specifications, but there is little room for error. Values above 1.33 are generally considered acceptable in many industries, while values above 2.0 indicate an excellent process capability.