People have different ideas of what it is, and it varies from more gentle methods of just creating a routine and a good environment to encourage sleeping, to trying to get them to self settle by being put to bed awake with timed intervals of crying before stepping in to comfort, to the more extreme which is called extinction sleep training. Extinction is putting them to bed awake at a set time and walking away until a set time in the morning. No going to check on them, no matter how much they cry. Sleep training of any kind usually discourages feeding to sleep. As a mum of twins, feeding to sleep was a goddamn life saver. Funnily enough they grow out of feeding to sleep on their own, and too soon if you ask me. I say use that magic tool while it works