By default, a spreadsheet cell reference is relative. What this means is that as a formula or function is copied and pasted to other cells, the cell references in the formula or function change to reflect the function's new location.
Alternatively, an absolute cell reference, such as $F$34 or $G$67, does not change when a formula or function is copied to other cells.
A mixed cell reference then, is a combination of relative and absolute cell references.
As with absolute cell references, the dollar sign ( $ ) is used in mixed cell references to indicate that a column letter or row number is to remain fixed when a copied from one cell to another.
Examples of a mixed cell reference would be $E4 or F$6.
For $E4, the column letter is fixed while the row number is allowed to change when copied to other cells. For F$6, the row number is fixed while the column letter changes.
Note: When listing any cell reference - relative, absolute, or mixed, the column letter is always listed first.