Which of the following is referred to as "for the sake of form"?

The term "pro forma" is used to describe actions taken or documents prepared for the purpose of legality or conformity, rather than for their inherent content or value. In many legal and business contexts, pro forma documents or procedures ensure that necessary forms are completed to meet formal requirements, even if they do not carry substantive weight. For example, a pro forma invoice provides a preliminary bill of sale and may be used to allocate funds or to provide an estimate, but it is not a formal demand for payment.

The other terms, while they have their own distinct meanings, do not convey the idea of fulfilling a requirement merely for the sake of formality. "Pro tem" refers to a temporary position or arrangement, “pro bono” signifies work done voluntarily and without payment, typically in legal contexts for the public good, and "post mortem" pertains to analyses conducted after an event has concluded, often in a medical or investigative setting. Thus, "pro forma" uniquely encapsulates the concept of actions taken purely to satisfy formalities.