A matrix (also called an array) is a rectangular set of numbers, called elements. The use of matrices is not part of this discussion, but a common operation is the multiplication of two matrices. A row is a line across the matrix, and a column is a line up and down. The dimension of a matrix is the number of rows and columns.

Example:   This matrix has dimension 3x4 ("three by four") because it has 3 rows and 4 columns. The two brackets on each side help identify what all is in the matrix. They can be just vertical lines, also.

Multiplying Matrices