NOPAT is Net Operating Profit After Tax. The measurement is a good way to understand the underlying profitability of a business by stripping away the effects of financing, since its primary focus is on earnings generated by operations.
It is effective when comparing the results of several companies in the same industry that employ different financing structures, since the results will exclude the effects of financing. Otherwise, the results of a highly leveraged company would likely be seen to spike or drop in relation to the results of other companies with more conventional financing structures.