A matrix which is not a square matrix is called a..........matrix.

Explanation

To solve the question, we need to define what a matrix is and differentiate between square matrices and non-square matrices.

### Step-by-Step Solution:

1. **Understanding Matrices**: A matrix is a rectangular array of numbers arranged in rows and columns. The size of a matrix is defined by its number of rows (m) and columns (n).

2. **Square Matrix Definition**: A square matrix is a type of matrix where the number of rows is equal to the number of columns (m = n). For example, a 2x2 matrix or a 3x3 matrix is square.

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