Final answer:
A workbook variable that can replace a constant value in a calculation, filter, or reference line is called a parameter. Parameters allow users to adjust values to see changes in scenarios or visualizations.
Step-by-step explanation:
In the context of a workbook, often used in spreadsheet applications or data visualization tools like Tableau, the correct term for a workbook variable that can replace a constant value in a calculation, filter, or reference line is a parameter. Unlike a constant, which is a fixed number, or a variable, which can change depending on the context within the program, a parameter is a flexible element that users can adjust to test different scenarios or to control inputs within calculations or visualizations. For example, if an equation of a line is given by y = mx + b, m and b might be constants in one instance but could also be turned into parameters if we wish to allow users to explore how changing these values affects the slope and y-intercept of the line.