Final answer:
An absolute cell reference requires the use of the dollar symbol ($), as in $A$1, to ensure the referenced cell does not change when a formula is copied.
Step-by-step explanation:
An absolute cell reference in a formula is indicated by the use of the dollar symbol ($).
This symbol is used before the column letter and/or row number to ensure that the specific cell reference does not change when the formula is copied or filled to other cells. In spreadsheet applications like Microsoft Excel, an absolute reference might look like $A$1, which means that both the column (A) and the row (1) will not change when the formula is copied.