Which term refers to the act of fulfilling or carrying into effect an agreement?

The correct answer is the term that specifically denotes the act of fulfilling or implementing an agreement, which is "Execution." This term is commonly used in legal and business contexts to describe the process of putting a plan, decision, or agreement into action. For instance, when a contract is signed, the execution phase begins, where the parties involved carry out the terms and conditions laid out in the contract.

While "Accomplishment" refers to the successful completion of a task or goal, it does not specifically address the procedural act of fulfilling an agreement. "Achievement" similarly pertains to reaching a desired goal but lacks the connotation of process that "Execution" provides. "Completion" indicates the end of a process or task but doesn’t capture the connotation of actively carrying out or implementing an agreement, making it less precise in this context.