It measures how open the throttle is. The engine computer uses this information to set fuel delivery and ignition timing, giving the engine the right response as you press or release the accelerator. Typically, a throttle position sensor is a small potentiometer attached to the throttle body. As the throttle plate moves with the pedal, the sensor’s contact moves along a resistive track, changing the voltage it sends to the ECU. In most systems this voltage ranges from near 0 volts when the throttle is closed to about 5 volts at wide-open throttle, and the ECU uses that signal to adjust fuel mixture, idle speed, and timing for smooth acceleration and efficient operation. Other terms like throttle pressure sensor aren’t standard names for this function, since that would imply measuring pressure rather than position. So the throttle position sensor is the correct designation.