Flexibility has become a key objectives in the design of manufacturing systems and a critical measure of total manufacturing performance. The need for flexibility is increasing due to some environmental change such as changing technical characteristics of the products and the changing nature of market demands. Most importantly, flexibility embodies competitive value for a manufacturer. Although the importance of flexibility has stressed in the various research, very few attempts have been made to synthesize the literature dealing with definitions and measure of flexibility. It is this issue that have motivated us to search for the definition and classification of flexibility.