Which term indicates a guideline that is advisable but not required?

The term that indicates a guideline that is advisable but not required is "should." In regulatory and standards documentation, "should" is commonly used to suggest a recommended practice or course of action that is considered to be beneficial and is strongly encouraged. However, it does not impose a mandatory requirement, allowing for the possibility of alternative approaches or methods that may also be acceptable under certain circumstances.

In contrast, "shall" conveys a strict requirement that must be followed, while "may" indicates permission to take a particular action, suggesting that it is optional. The term "can" refers to the capability or possibility of doing something, which does not imply recommendation or obligation. Thus, "should" specifically denotes an advisable action without being obligatory, making it the correct choice in this context.