Which of the following best describes fraud in contract law?

Fraud in contract law primarily refers to deceptive practices that are intended to secure an unfair or unlawful advantage in a transaction. This definition emphasizes the intentional aspect of fraud—where one party knowingly misrepresents information or conceals material facts with the goal of misleading another party into entering a contract. By understanding fraud in this way, it becomes clear that the act is not just about misinformation but also about the underlying intent to benefit illegitimately from the deception.

The other options do not encapsulate the essence of fraud as effectively. For instance, agreement on the same thing in the same sense pertains more to mutual assent in contract formation and does not involve deception. A contract that can be rescinded by the aggrieved party could happen under various circumstances, including but not limited to fraud, but it does not define fraud itself. Lastly, if only one party is mistaken about a fact, it suggests a misunderstanding rather than an intention to deceive, which is a critical element of fraud. Thus, the focus on deception in the correct answer aligns seamlessly with the legal understanding of fraud in the context of contracts.