\begin{definition}[Definition:Matrix/Square Matrix]
An $n \times n$ matrix is called a '''square matrix'''.
That is, a '''square matrix''' is a matrix which has the same number of rows as it has columns.
A '''square matrix''' is usually denoted $\sqbrk a_n$ in preference to $\sqbrk a_{n n}$.
In contrast, a non-'''square matrix''' can be referred to as a '''rectangular matrix'''.
\end{definition}