An Expert Advisor, not to be mistaken for a human specimen of any kind, is the name given to bits of software installed on MT4 trading platform, written in the proprietary MT4 programming language (file ending “.mql”).
Some traders call an Expert Advisor (short: “EA”) a trading robot, and this is not far from the truth.
Expert Advsiors may be used to assist and complement a human trader, for example to sound warnings or prevent exceeding certain limits.
However, Expert Advisors are also used for fully automated trading. You can hire a dedicated programmer to make an EA for you, or subscribe to a signal, thus implementing the EA’s commands onto your MT4 platform’s activity.
It is advisable to never mix complex EA’s or use several unrelated EA’s on one and the same MT4 terminal. Instead, spread your capital across several smaller accounts, and allow multiple EA’s to generate profit for you separately.