A closed-market transaction is simply an order placed by an insider according to the rules and regulations set out by the SEC. With a closed-market order, the insider is buying or selling shares at a price above or below the market and directly from and to the company rather than openly on the market. These types of inside trades are generally not considered significant as they do not reflect the insider's sentiment towards the company.
Here's an example of a closed-market transaction: an insider is given the stock of a subsidiary company, and then he or she immediately sells the stock.