cost coefficient

The updated coefficients, also known as relative cost coefficients, are the rates of change of the objective function with respect to the nonbasic variables.

So, in the case of a cost-minimization problem, where the objective function coefficients represent the per-unit cost of the activities represented by the variables, the "reduced cost" coefficients indicate how much each cost coefficient would have to be reduced before the activity represented by the corresponding variable would be cost-effective.