This is mostly correct. The Prius is actually a series-parallel hybrid, as it maintains a direct mechanical link between the engine and the wheels (and the engine is capable of adding power to the wheels) but it also uses two electric motors to isolate the two degrees of freedom (engine rpm and wheel speed). This second part is the series bit: the wheels and the engine are, in principle, fully independent, because the motors can absorb or add power to the crankshaft and the driveshaft to hit a target rpm without changing the rpm of the other shaft. In practice, the Prius doesn't run at a constant rpm due to sizing constraints of the motors, as the mechanical linkage means that one motor has to be able to absorb the engine power and torque of the other motor, which is impossible across all conditions.

Most hybrids are actually parallel or series-parallel. Series hybrids are comparatively rare because the traction motor has to be sized for the full operational range of the vehicle. Their primary advantages are mechanical simplicity and packaging; even though the power electronics and motors are bigger, the lack of mechanical coupling means you can put them wherever is convenient.