Each tank or device in vaping has a way it draws similar to a cigarette a roll your own can be a tighter draw depending on how you roll it and a silk cut maybe a looser draw because of the extra hole in the filter
Mouth to Lung (MTL) is used to describe when the user takes the vapour into their mouth and then inhales it into the lungs. This is the most common way people vape or smoke
Direct to Lung (DTL) is used to describe when the user takes the vapour straight into the lungs bypassing the mouth. This type of draw is used to create bigger vapour clouds.
Restricted Lung Inhale is used to describe when a device is capable of both a mouth to lung inhale and a more restricted direct to lung inhale giving a best of both worlds in some peoples opinion.