Which term describes intentionally causing damage to someone else's contractual relationship?

The term that describes intentionally causing damage to someone else's contractual relationship is tortious interference. This concept in law arises when one party deliberately disrupts the contractual relationship between two other parties, typically by persuading one of the parties involved to breach the contract or by creating conditions that make the contract unfulfillable.

Tortious interference can occur in various contexts, such as persuading a business partner to withdraw from a contract, spreading false information to cause a party to break an agreement, or any other actions that intentionally lead to the disruption of a contractual relationship. A key element of tortious interference is the intention behind the actions; it is not just a matter of negligence or an innocent mistake, but rather a willful act aimed at harming that relationship.

Other terms mentioned, such as negligence, defamation, and fraud, describe different legal issues that do not specifically align with the act of deliberately damaging someone else's contractual ties. Negligence pertains to failing to act with reasonable care, defamation involves damaging someone's reputation through false statements, and fraud involves deceitful practices intended to secure unfair or unlawful gain. These do not encapsulate the focused nature of tortious interference, making this answer the most accurate in the context of the question.