Mac OS X features a built-in app called the Terminal. It allows users to interact with their computer using text-based commands. The Terminal comes in handy to tweak the system settings, troubleshoot your computer, or perform tasks that would otherwise require additional software. While the Terminal is often of no interest to the casual Mac user, it remains an invaluable tool for power users.
Warning: You should be very careful when using the Terminal as the slightest mistake could lead to irreversible damage (system failure, boot issues, crashes, slowdowns, or data loss).