High-Frequency-Trading (HFT) is a type of fast trading where computers make quick decisions to buy and sell stocks. HFT traders use algorithms to analyze market data and make trades in a fraction of a second. They focus on short-term profits by taking advantage of small price differences in the market. HFT requires fast reaction times and low delays to be successful. This type of trading has become more common in recent years, especially after the 2010 "Flash Crash" and during the financial crisis.