Automated trading
An automated trading system (ATS) is a computer program that creates orders and automatically submits them to a market center or exchange.
Automated trading systems are often used with electronic trading in automated market centers, including electronic communication networks, "dark pools", and automated exchanges. Automated trading systems and electronic trading platforms can execute repetitive tasks at speeds with orders of magnitude greater than any human equivalent. Traditional risk controls and safeguards that relied on human judgment and manual speeds that were appropriate to manual and/or floor-based trading environments, must now be automated to evaluate and control automated trading.
As of 2014[update], more than 75 percent of the stock shares traded on United States exchanges (including the and NASDAQ) originate from automated trading system orders. ATSs can be designed to trade stocks, options, futures and foreign exchange products based on a predefined set of rules which determine when to enter an order, when to exit a position and how much money to invest in each trading product. Trading strategies differ; some are designed to pick market tops and bottoms, others to follow a trend, and others involve complex strategies including randomizing orders to make them less visible in the marketplace.
Backtesting of a trading system involves programmers running the program using historical market data in order to determine whether the underlying algorithm guiding the system may produce the expected results. Developers can create backtesting software to enable a trading system designer to develop and test their trading systems using historical market data to optimize the results obtained with the historical data. Although backtesting of automated trading systems cannot accurately determine future results, an automated trading system can be backtested using historical prices to see how the system theoretically would have performed if it had been active in a past market environment.
...
Wikipedia