ECU Remapping is the process of modifying the software in a vehicle's Engine Control Unit (ECU) to enhance performance. This involves changing parameters such as fuel injection, ignition timing, and boost pressure to optimize engine efficiency and power output. By adjusting these settings, drivers can experience improved acceleration, better fuel economy, and a more responsive throttle. However, it's important to note that improper remapping can lead to engine damage or void warranties, so it should be done by a qualified professional using reliable software.