What term is used to indicate an essential operating or maintenance procedure?

The term used to indicate an essential operating or maintenance procedure is "note." In the context of operating manuals and maintenance guidelines, a note typically highlights crucial information that must be observed for the safe and effective use of equipment. It serves as a direct reminder of specific actions or precautions that need to be taken, ensuring that the user adheres to important protocols that can affect operation or safety.

In contrast, while a guide may provide overall instructions or broader context, it does not specifically point out critical procedures. A tip usually offers advice or suggestions that enhance performance but might not indicate essential actions. A reminder helps jog memory but is not typically associated with essential procedures in the same definitive way a note is. Thus, "note" is the most appropriate choice for highlighting essential operating or maintenance procedures.