Program traing is casually defined as the use of computers in stock markets to engage in arbitrage and portfolio insurance strategies. However, the New York Stock Exchange (NYSE) defines the term as "a wide range of portfolio trading strategies involving the purchase or sale of 15 or more stocks having a total market value of $1 million or more" without any direct reference to the use of computers. The word "program" can be interpreted in its earlier, more general meaning of a defined and pre-arranged sequence of steps, rather than specifically a computer program. Some program trading strategies are subject to regulatory restrictions. For instance, NYSE Rule 80A requires index arbitrage trades to be marked when submitted.