High-frequency trading is a class of algorithmic trading strategies characterized by the use of sophisticated technological infrastructure and low-latency connections to financial exchanges to execute a large volume of orders at extremely high speeds, frequently within fractions of a second. As an academic concept and research area, it investigates the design, implementation, and market impact of these strategies, including their effects on market microstructure, liquidity provision, price formation, volatility dynamics, and the broader implications for financial market stability and regulation.