Which of the following terms refers to a party's undertaking to indemnify another against loss?

The term that refers to a party's undertaking to indemnify another against loss is "insurance." Insurance is a contractual arrangement where one party (the insurer) agrees to provide financial compensation to another party (the insured) in the event of specified types of loss or damage. This contractual relationship is designed to protect individuals or entities from financial burdens that might arise from unforeseen circumstances, such as accidents, natural disasters, or health issues.

In the context of the other options, "ensure" generally refers to making certain or guaranteeing a particular outcome, but it does not inherently involve indemnification. "Contract" is a broader term that describes any agreement between parties, which may include various obligations and rights but does not specifically denote the aspect of indemnification. "Liability" pertains to the legal responsibility for one's actions or omissions, which can create a obligation for indemnification but is not an undertaking itself to provide financial protection against loss. Thus, "insurance" is the most accurate term that embodies the concept of indemnification against potential losses.