Virtual Metrology (VM):

Virtual Metrology is a concept to predict physical and electrical parameters of wafers and/or devices from information collected in real time from the manufacturing tools (e.g., equipment or process parameters) and from other available sources (e.g., production context information or up-stream metrology). Benefit: virtual measurements can be done where integrated metrology is not available, not feasible, or too expensive. VM enables wafer-to-wafer or even die-to-die control.