What is the difference between high bypass and low bypass turbofan?

The difference between the low and high bypass turbofans is simply in the amount of air which goes into the engine versus the remainder that goes around (bypasses) the engine.

In high bypass engines ( an engine on any large commercial jet) only 20% around 20% of air goes into the engine with 80% bypassing it. (The 80% generates most of the engine thrust)

In low bypass engines, this ratio is much lower