Final answer:
In Excel, the AutoFill function is used to automatically fill in the missing cells with sequential values or patterns by dragging the fill handle of the selected cell or range.
Step-by-step explanation:
The method applied in Microsoft Excel to automatically fill in the missing cells below an initial cell or range with sequential values or patterns is called AutoFill. This feature is particularly useful for populating a column or row with a series of values, such as days of the week, months, numbers, or even custom lists. To use AutoFill, you simply need to select the cell or range from which you want to extrapolate, then click and drag the fill handle (a small square at the bottom-right corner of the selection) down or across the cells you wish to fill.