What is an accepted collection of requirements and recommendations for materials and services?

The term that accurately describes an accepted collection of requirements and recommendations for materials and services is "Standard." Standards provide a framework that guides industry practices, ensuring consistency, safety, and quality across various applications. They are typically developed by recognized organizations and can encompass a range of topics, from product characteristics to testing methods and performance criteria.

In contrast, "Code" usually refers to a set of regulations or laws that must be followed, often pertaining to safety and legal compliance, rather than a broader collection of recommendations. "Specification" refers to detailed descriptions of certain aspects of materials or services needed for a project but may not encompass the broader set of requirements and recommendations that a standard provides. "Protocol," while it can indicate a series of established procedures, usually pertains to specific processes rather than the overall requirements and recommendations for products and services. Thus, "Standard" is the most fitting term in this context.