What does OD on a car mean?

[OHarrison]

OD on a car stands for Overdrive, and its button is usually located on the gear lever, with the exact position varying by vehicle model. Overdrive is primarily used in non-manual automatic transmissions, serving to limit the gear from shifting into overdrive, thereby keeping the gear within 1st, 2nd, or 3rd to facilitate quick overtaking. When the OD button on the gear lever is pressed, the dashboard will display an "OD off" indicator, meaning the transmission will not engage overdrive (i.e., it won't shift into 4th gear) and will only switch between 1st, 2nd, and 3rd gears. When driving at high speeds and needing to overtake, for vehicles with a 4-speed automatic transmission, the transmission typically shifts into 4th gear during highway driving, which is the overdrive state. Pressing the OD button to downshift to 3rd gear increases the engine RPM and torque, allowing for quicker acceleration and overtaking when the throttle is pressed.