OBD, or On-Board Diagnostics, is a system used in vehicles to monitor and report on the performance of the engine and other essential components. It helps identify issues by generating diagnostic trouble codes (DTCs) when a problem is detected, allowing mechanics to quickly pinpoint and address malfunctions. The OBD system has evolved over the years, with OBD-II being the most common standard in modern vehicles. This version provides more detailed information and allows for better communication between the vehicle and diagnostic tools, improving maintenance and emissions control efforts.