as title, im curious to learn what it actually is

 

It is basically the number of entries into a turbo, 2.

The long answer is the turbo is divided into 2 separate entries each fed by 2 cylinders which are kept separate. By doing this each pulse from the cylinder is concentrated onto the exhaust turbine and produces more energy upon it alowing earlier spool.

The downside to twinscroll is it makes the exhaust housing smaller by dividing it and can then loose top end power