Experimental domain: the experimental ‘area’ that is investigated (defined by the variation of the experimental variables). Factors: experimental variables that can be changed independently of each other Independent Variables: same as factors Continuous Variables: independent variables that can be changed continuously Discrete Variables: independent variables that are changed step-wise, e.g., type of solvent. Responses: the measured value of the result(s). from experiments Residual: the difference between the calculated and the experimental result