An EX4 file is a compiled program written for MetaTrader, an platform created for online trading of Forex, Futures, and CFD markets. It contains executable code that has been compiled from .MQ4 files and can be executed on the MetaTrader platform.

EX4 files are compiled by Meta Editor, which is included with the MetaTrader software, from source code files. The EX4 file may contain indicators, scripts, or an Expert Advisor, which is a program for automating the trading and analytical processes in MetaTrader. The EX4 file is used by MetaTrader 4, while the .EX5 file is used by MetaTrader 5. To open an EX4 file in MetaTrader 4, the file must be placed in the "Indicators" folder. You can then open the file by clicking the Editor tool in the MetaTrader 4 toolbar, selecting the "Indicators" folder in the left "Navigator" panel, and then choosing the appropriate EX4 file.