no lockup is completely different, Overdrive is actually a gear selection and has a ratio of less than 1:1, if the ratio is 0.5:1 - that means the engine spins 1 time for every 2 spins of the transmission output shaft. (the reason I said 0.5 or 0.7 was that different transmissions have different ratio setups)
Lockup of the convertor is quite modern and in it there is a one way clutch inside the convertor that locks drive to the turbine. This is done to prevent slip losses of the convertor which are usually 10% in any case. This enhances fuel economy further but adds another shift system to the transmission, which itself has its pros and cons.