Final answer:
In the formula =$C$5*D$15 from cell D15, the D$15 is a Mixed Reference, combining absolute reference for the row and relative reference for the column.
Step-by-step explanation:
If cell D15 contains the formula =$C$5*D$15, the reference to D15 in the formula is a Mixed Reference. A mixed reference is a cell reference that contains both absolute and relative references. In this case, $C$5 is an absolute reference, meaning it is locked both column 'C' and row '5' and will not change no matter where the formula is copied to. On the other hand, the D$15 part of the formula implies that the column 'D' is relative and can change if the formula is moved horizontally to another column, but the row '$15' is absolute, meaning it will not change if the formula is copied to another row. This mixed reference combines the flexibility of relative referencing with the consistency of absolute referencing where necessary.