Step 1: Concept of interest on drawings.
Interest on drawings refers to the amount paid by the partner to the firm for the use of capital withdrawn from the firm.
Step 2: Accounting treatment.
Interest on drawings is considered an income for the firm, as the firm earns it from the partner.
Step 3: Conclusion.
Thus, the correct answer is (C) Income.
Final Answer:
\[
\boxed{\text{Income}}
\]