It stands for market on close; an order that is placed with a broker of securities or commodities by a trader (market participants) requesting the purchase or sale to be filled at the final closing price for the day’s trading session. It is a non-limit market order, which is typically executed at or as near to the closing price as possible, depending on market conditions. Brokers attempt to fulfill MOC orders, but in extremely volatile markets, execution at the final closing price might not be possible.

This type of order may involve trading of instruments stocks, options, or futures, or even underlying assets (commodities), as close as possible to the market close.

Orders that are intended to be filled on the other end of a trading session are known as market on open (MOO).