Net Operating Profit After Tax (NOPAT) is a way to measure profits that excludes the impact of debt financing (via tax benefits and costs).
The easiest way to think about Net Operating Profit After Tax is as a company’s profit if it were unleveraged, i.e., if it had no debt. There are costs associated with debt but also tax benefits, so there’s some give and take.
The reason an analyst might use NOPAT is to gain a more accurate look at the operating efficiency of a leveraged companies, since it excludes the tax savings many companies get because of existing debt.