Well, you know what interest cost is, right? You have $300 million in debt and you pay 6% interest on it. So...this year's cost? Yep: $18 million.
What's that tricky "net" doing in there then? Well, it turns out that you also had $100 million in cash, just sitting around in a money market account, earning 2%. That cash earned you $2 million in interest to you, the "bank." So wait. You have $18 million in gross interest costs, but then you subtract $2 million in cash accruing to you...so you then have $16 million in net interest cost. A bit easier to digest.