Which term is used to indicate an obligation in plain language guidelines?

The term that indicates an obligation in plain language guidelines is "Must." This term is used to convey a requirement or necessity, signifying that something is not optional but rather a definitive mandate that must be followed. In the context of plain language guidelines, using "Must" ensures that the reader understands that compliance with the stated guidelines is essential.

In contrast, "May" suggests permission or a possibility without any obligation, meaning that the action isn't required. "Should" typically implies a recommendation or best practice rather than a strict requirement, so it allows for exceptions. "Can" indicates capability or ability, conveying that something is possible but not necessarily required.