Box 16d represents s distribution of assets. Distributed assets are are not income to you until you sell your distributed share, but they can reduce your cost basis in the Corp.
If, for example, if your S Corp owned a warehouse , it might distribute that asset to one or more shareholders rather then selling it. If your basis, or cost in the Corp included that asset originally, the distribution would affect the cost basis you now have in your Corporation for the time when you might sell your shares to another entity.
Ordinary income is that year's income that was derived by conducting the regular business of the partnership.
Another very simple example might occur if the S Corp originally purchased and now operates an antique store. Ordinary income stems from the operation of the store. The owners might, though, have a rare antique that they choose to distribute to shareholders rather then hold as inventory and sell in the store. That distribution doesn't change the year's profit from the store but would change the basis of the shares owned by the shareholders.
