Definition:Off-Diagonal Element

Definition
Let $\mathbf A = \sqbrk a_{m n}$ be a matrix.

The off-diagonal elements of $A$ are the elements of $\mathbf A$ which do not lie on the main diagonal of $\mathbf A$.

That is, the elements $\map a {r, s}$ where $r \ne s$.

That is, the elements of $\mathbf A$ which are not diagonal elements.