Final answer:
Closed brackets in Excel's formula guidance denote a closed function or argument, indicating the grouping and structure of a formula's components for proper calculation.
Step-by-step explanation:
When Excel displays formula guidance, the closed brackets typically denote a closed function or argument. In this context, closed brackets are used to group certain parts of the formula to clarify the order in which operations should be performed and can indicate where a function's arguments begin and end. This helps the user understand how the different parts of the formula are structured and ensures the correct calculation is made.