What defines the relationship in which rights and responsibilities are established implicitly rather than explicitly?

The correct choice is the concept of implied contractual terms, which refers to the arrangement where rights and responsibilities of parties are established based on their conduct, circumstances, and various legal principles rather than through clear, explicit written or spoken agreements.

In many legal contexts, the behavior of parties can create obligations even when there is no formalized contract. For instance, if two parties engage in a transaction where one party consistently performs duties that the other party relies upon, the law may infer certain terms and conditions based on these actions. This can often be seen in relationships where contracts are not formally documented, but a consistent pattern of interaction establishes expectations and duties that are enforceable.

Other options, such as explicit agreements and formal contracts, involve clear, documented terms that are either written or verbally communicated, which does not align with the scenario described in the question. Unwritten rules could imply norms or social expectations but don’t encompass the legal aspect of implied contracts, which carry enforceable obligations under the law. Thus, implied contractual terms best fit the definition of establishing a relationship where rights and responsibilities exist without explicit agreements.