To continue studying or exercising (some thing) after preliminary proficiency is attained to be able to reinforce or ingrain the learned product or skill.
to understand (an undeniable fact or skill) repetitively, beyond the stage where it could be straight away recalled; in experimental therapy, to continue to learn beyond the point where the criterion of sufficient understanding has-been achieved.
To learn (one thing) more than is necessary; to review excessively, to just take (some thing) too much to heart.
To learn (something) to the point in which responses come to be instinctive.
Mostly when talking about neural companies, to understand an activity to the stage in which responses in fact start to break down. Compare with overfit, in design tuning contexts.