what is Shimano HG and HG+

We heard shimano HG chain or HG freewheel often ,even  HG+ ; so what is it ?  

In early times ,the transmission system need to completely detach from the old gear then get on the new gear ; that takes too much time . So Shimano thinks , is there any way to make it faster ?  Is it possible to let the chain shift in new gear before it completely detach from the old gear ?

After many experiment , the HyperGlide was invented . This petant is to carve grooves in special places on the gear ( freewheel or chainwheel ) , This can allow the chain shift into a new gear quickly and won't interrupt the power while riding .

But attention , if you are shifting to lower gear that will be smooth , when you shift to higher gears with power on , that might be a little vibration if you don't interrupt the power . if you want to avoid this vibration , you need HG+ petant , this petant just available above deore level ; a littttttle expensive .

As i said the HG and HG+ is a petant , so it applies to products like HG freewheels / HG chain / HG chainwheel .