Engine most commonly used around the world. although on a dirt bike they perform terrible because compared to a 2 stroke, they put out more torque rather than HP and torque is not really needed on a 150 lb machine to get up to speed.
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.