A command interpreter is software that reads commands and runs them, usually through a shell or terminal. It accepts text typed by a user or pasted from another source, then translates that text into actions the operating system can perform. On macOS, Terminal is a common example of a command-line interface that uses a command interpreter behind the scenes.
In cyber security, command interpreters matter because they turn plain text into execution. That makes them a frequent target in social engineering: attackers may trick a user into pasting a one-line command that downloads payloads, launches scripts, or changes system settings. Defenders watch for suspicious shell activity, unusual process trees, and risky copy-and-paste prompts, because the danger is often not a malicious file but a malicious instruction. Treat any webpage that asks you to run a command as a potential attack surface.