Step 1: Analyze the terms.
- At par, At premium, and At discount refer to the terms used in the context of bonds, shares, or securities trading.
- At loan refers to borrowing money, which is unrelated to the trading or valuation of securities.
Step 2: Conclusion.
Therefore, At loan is the odd one out, as it does not relate to the trading of securities.
Final Answer: \[ \boxed{At \; loan} \]