To solve this question, the user needs to have knowledge of LoadRunner and its terminology.

The term for varying values defined in a placeholder that replaces hard-coded values is called a parameter.

Option A, variable, is incorrect because although variables can hold changing values, they are not specifically used to replace hard-coded values.

Option B, constant, is incorrect because constants, by definition, are values that do not change. They are not used to replace varying values.

Option D, correlation, is incorrect because correlation is a technique used to handle dynamic values in web applications, but it does not replace hard-coded values like a parameter does.

Therefore, the answer is:

The Answer is: C. Parameter