Oh look, Trekk's back! FWIW, in SAE (Society of Automotive Engineers) terms, it's referred to as a "flexplate"...and yup, they sometimes "let-go"! PK nailed it, in that it is the "replacement" for the flywheel in an automatic trans application allowing for not only a mounting point for the starter ring gear but to also allow for minor misalignment issues between the transmission and crankshaft (the domain of the clutch plates in a manual trans application), hense the name "flexplate". The torque converter takes the place of the manual transmission-required flywheel, providing enertia to smooth-out the engines combustion pulses as well as a torque-buffer between the engine and transmission. The more you know !!