An automatic transmissions flexplate is a metal disk that connects the output of your motor to the torque converter. In a manual transmission this disc is known as a flywheel. As the flexplates name implies it has the actual ability of flexing across allowing to take up motion in the torque converter as the speeds change. There are weighted and non-weighted
flexplates available. On the flexplate you will notice teeth around the outer edge. These teeth allow engagement with the vehicle's starter allowing it to start.