A reference identifies a cell or a range of cells on a worksheet and tells where to look for the values or data you want to use in a formula. With references, you can use data contained in different parts of a worksheet in one formula or use the value from one cell in several formulas. You can also refer to cells on other sheets in the same workbook, to other workbooks, and to data in other programs. References to cells in other workbooks are called external references. References to data in other programs are called remote references.
Relative vs. absolute references Depending on the task you want to perform in Excel, you can use either relative cell references, which are references to cells relative to the position of the formula, or absolute references, which are cell references that always refer to cells in a specific location. If a dollar sign precedes the letter and/or number, such as $A$1, the column and/or row reference is absolute. Relative references automatically adjust when you copy them, and absolute references don't.
Labels and names You can use the labels of columns and rows on a worksheet to refer to the cells within those columns and rows. Examples of labels are "Price," "Quantity," and "Total." Or you can create descriptive names to represent cells, ranges of cells, formulas, or constant values.
3-D references If you want to analyze data in the same cell or range of cells on multiple worksheets within the workbook, use a 3-D reference. A 3-D reference includes the cell or range reference, preceded by a range of worksheet names. Excel uses any worksheets stored between the starting and ending names of the reference. For example, =SUM(Sheet2:Sheet13!B5) adds all the values contained in cell B5 on all the worksheets between and including Sheet 2 and Sheet 13.