Absolute cell references in Excel are denoted by a \$ sign before the column and/or row. For example:
\[
\text{Absolute Reference: } \$A\$1
\]
Mixed references, on the other hand, have a \$ sign before either the row or column but not both. For example:
\[
\text{Mixed Reference: } \$A1 \, \text{or} \, A\$1
\]