The absolute complement of a set A refers to all the elements in the universal set U that are not in A. It represents what is "outside" set A relative to the universe being considered.
\[ A' = U \setminus A \]
Where:
\[ U = \{1, 2, 3, 4, 5, 6, 7\}, \quad A = \{2, 4, 6\} \] \[ A' = \{1, 3, 5, 7\} \]