Algorithmic Trading

What Does Algorithmic Trading Mean?
A trading system that utilizes very advanced mathematical models for making transaction decisions in the financial markets. The strict rules built into the model attempt to determine the optimal time for an order to be placed that will cause the least amount of impact on a stock's price. Large blocks of shares are usually purchased by dividing the large share block into smaller lots and allowing the complex algorithms to decide when the smaller blocks are to be purchased.

Investopedia explains Algorithmic Trading
The use of algorithmic trading is most commonly used by large institutional investors due to the large amount of shares they purchase everyday. Complex algorithms allow these investors to obtain the best possible price without significantly affecting the stock's price and increasing purchasing costs.