An executable is a type of computer file that contains instructions for a computer to perform specific tasks or run a program. When you open or double-click an executable file, your computer automatically starts the associated software or process without needing further input. Executables are commonly used to install applications or launch programs and typically have file extensions like .exe on Windows or .app on macOS. Because they can make changes to your system, it's important to only run executables from trusted sources to avoid malware or other security risks.