To make good is to repay a debt, financial or otherwise. You can make good on a loan, on a promise, on a business deal. You can make good a construction site after the work's done to return it, more or less, to the state it was in before work started. Regardless of the mostly benign nature of the idiom, it still doesn't sound at all out of place coming out of the mouth of a loan shark.
In the advertising world, it's a noun. A 'Make Good' is an advertisement that's run to even out a deficit.
It works like this: ads are sold based on potential. A network pulls together statistics on who exactly is watching any given piece of programming and breaks it down demographically by age, ethnic background, median income and the like, and sets a price based on how many eyeballs are tuned into the show with the sweet spot (usually males aged 18-35 with high levels of expendable income) being weighted more in the final analysis - it's why ad time in the superbowl is so fantastically expensive. The more attractive people (not physically; demographically) watching a program, the more each block of advertising time costs. If you think that's a little counterintuitive, just wait.
The problem is that all this ad time has to be sold in advance, and the actual performance of a show can be drastically different from how well the numbers predicted it would. If a show actually does better that it was supposed to, the advertisers are happy - they got eyeballs for free, and next year the networks will try to narrow the gap by making their statistics more accurate. If it does worse, the advertisers are unhappy because they paid for impressions they didn't get, and the networks are unhappy because, though they made more money than they 'deserved,' the cash won't be staying in the bank for very long.
If the networks don't deliver, they have to provide time for 'Make Good' advertisements in the next cycle. Essentially, coming in under their projections means they need to give free commercial time to their advertisers in the next cycle to make up for the impressions they didn't deliver last time. Every block of time they have to give away is a block of time they could be selling. Make Goods are bad for pretty much everyone, and advertisers and networks alike spend millions of dollars a year on marketing research firms to guarantee, so far as they can, that they don't happen.