There are different types of hybrid cars/hybrid automobiles

1) Series Hybrid :In a series hybrid, gasoline engine is used to turn the generator. The generator then either charges the batteries or powers the electric motor, which then drives the transmission. The internal combustion engine is used as an on-board generator to supply power to the electric motor which provide the sole driving force to the wheels.

2) Parallel Hybrid: In a parallel hybrid, a fuel tank powers a gas engine and batteries power an electric motor, then both the motor and the engine turn the transmission, which turns the wheels. In a parallel hybrid, a small 4-cylinde engine is used to make it fuel efficient. The batteries store the energy from regenerative braking mechanism and also from the energy generated from the motor. The internal combustion engine drives the wheels directly with the electric motor serving as a power assist. The additional power available from the electric motor enables the manufacturers to reduce the size of the engine, which results in fuel economy.

Both types have some disadvantages leading to the latest type of the hybrid technology.

In this latest design, the wheels can be driven by either the electric motor or by an internal combustion engine using a planetary gear system to draw power from either source. In the models such as Toyota PRIUS, the on-board computer optimizes the fuel usage by shutting off the internal combustion engine when the electric motor is sufficient to provide the power. The internal combustion engine starts up only when extra power is needed or the battery needs recharging. The electric motor serves as the main driving force and generator in this latest design which is available in cars released in 2004 and later.

3) Full Hybrid: A full hybrid or strong hybrid is an automobile that can run just on engine, just on batteries or a combination of both energies. Examples of full hybrid are : Toyota PRIUS, Ford Escape. Toyota Prius can be all electric at lower speeds. So if you are driving slowly ideally you are not using any gas.

4) Assist hybrids: The assist hybrid is a type in which the automobile uses a battery and electric motors to accelerate the car in combination with an internal combustion engine. Example of assist hybrids are: The Honda Insight.

5) Plug-In hybrids : Plug-in hybrid are the ones that are able to run only in electric-only mode by using larger batteries and the ability to recharge from the electric grid. They are also called gas-optional, or gridable or plug-in hybrids. They go with general acronym-PHEV(Pneumatic hybrid electric vehicle).
The advantage offered by plug-ins hybrids is gasoline-independent driving for shorter distances and daily usages with extended hybrid facilities for long journey.

6) Mild Hybrids: In a mild hybrid the gasoline engine provides the main drive power and an electric motor helps give the car additional power when needed.