What is Algorithmic trading, high-frequency trading?

Algorithmic trading is trading in which a computer algorithm determines the parameters of orders (whether to send them, their timing, price or quantity, how to manage them afterwards) with little or no human intervention. High-frequency trading is algorithmic trading that relies on infrastructure minimising latency (co-location, proximity hosting or high-speed direct access), decides without human intervention for individual orders, and sends many orders, quotes or cancellations within the day.