Dimensions of a Matrix

To count matrices you count row X column

This matrix is one row by three columns, so it is a 1 x 3 matrix.

This matrix is three rows by three columns, so this is a  3 x 3 matrix.
This matrix is a square matrix.

This matrix is three rows by two columns, so it is a 3 x 2 matrix.

This is another three rows by three columns, so this is a 3 x 3 matrix.
This is an identity matrix.