Sleep training is teaching your little one how to fall asleep and fall BACK to sleep without being dependent on anything external such as rocking, feeding, or bouncing to sleep.
Sleep training is different from night-weaning. Under 6 months old we don't need to remove night feedings to teach our babies how to sleep through the night. This will just come as the baby no longer associates feeding with sleep. After 6 months old we might need to address night wakings as part of our goal of sleeping through the night.