Refers to computerized trading using proprietary algorithms. There are two types algo trading. Algo execution trading is when an order (often a large order) is executed via an algo trade. The algo program is designed to get the best possible price. It may split the order into smaller pieces and execute at different times. The second type of algo trading is not executing a set order but looking for small trading opportunities in the market. It is estimated that 50 percent of stock trading volume in the U.S. is currently being driven by algo trading. Also known as high-frequency trading.