What is unbalanced assignment problem?

If number of jobs is not equal to the number of operators then the assignment
problem is known as unbalanced assignment problem. In other words in a pay off
matrix of assignment problem if number of rows and number of columns are not
equal then it is unbalanced assignment problem.
To solve unbalanced assignment problem it is necessary to insert dummy row or
dummy column such that the given pay off matrix become a square matrix. All
values in dummy row or column are assume to be zero.