A program trading platform that uses powerful computers to transact a large number of orders at very fast speeds. High-frequency trading uses complex algorithms to analyze multiple markets and execute orders based on market conditions. Typically, the traders with the fastest execution speeds will be more profitable than traders with slower execution speeds. As of 2009, it is estimated more than 50% of exchange volume comes from high-frequency trading orders.






Taobiz explains High-Frequency Trading - HFT
High-frequency trading became most popular when exchanges began to offer incentives for companies to add liquidity to the market. For instance, the New York Stock Exchange has a group of liquidity providers called supplemental liquidly providers (SLPs), which attempt to add competition and liquidity for existing quotes on the exchange. As an incentive to the firm, the NYSE pays a fee or rebate for providing said liquidity. As of 2009, the SLP rebate was $0.0015. Multiply that by millions of transactions per day and you can see where part of the profits for high frequency trading comes from.

The SLP was introduced following the collapse of Lehman Brothers in 2008, when liquidity was a major concern for investors.