Affirmative Obligation

There's a position on the New York Stock Exchange called a specialist. These people facilitate the trading of stocks, making it possible to buy and sell stocks at all times.

They have certain responsibilities, including what is called an "affirmative obligation." This means that they must make sure there is a market for stocks, even if things start to get weird in terms of supply and demand.

So if you are selling a stock that no one wants to buy, the specialist will buy it themselves to ensure that trading continues in an organized way. Similar deal if you are buying stocks that no one wants to sell. The affirmative obligation assigns responsibility for maintaining an orderly market to the specialist, keeping trading going when supply and demand get out of whack.