1- Statistical definition: a statistical measure of the inherent process variability for a given characteristic. The most widely accepted formula for process capability is the 6 sigma range of common cause variation for statistically stable processes only.
2 - Manufacturing process definition: a measure of the manufacturability of a product considering availability of desired manufacturing processes, support or workpiece size, equipment characteristics (e.g., speeds, feeds, tonnage, etc.), and statistical capability as defined above.
Process capability is measured with the indices Cp and Cpk.