An imprint is a significant event from the past in which you formed a belief, or a cluster of beliefs. Every form of healing, whether physical or psychological, that I know of gives credence to the fact that present behaviors are often created or shaped by past behaviors and past events. What's important to us as NLP practitioners about past experiences is not the content of what happened, but the impression or belief that the person built from the experience.

The notion of imprinting comes from Konrad Lorenz, who studied the behavior of ducklings when they hatched. He discovered that baby ducks would imprint a mother figure in the first day or so of life. They did that by sorting for movement, so that if something moved just after they hatched from their eggs, they followed it and it "became" their mother. Lorenz would move, and the ducks would follow. He found that if he reintroduced them to their real mother later, they would ignore her and continue to follow him. In the morning, when he got up, he would go outside and find the ducklings curled up around his boots, instead of in their own nest. He once reported that a ping pong ball rolled by one of the eggs when it hatched and the emerging duckling imprinted to the ping pong ball, making it the "mother." Later in life, the duck would shun others of its own species at mating time and try to mount various kinds of round things.

Konrad Lorenz and his colleagues believed that imprints were established at certain neurologically critical periods, and that once the critical period had passed whatever had been "imprinted" was permanent and not subject to change. Timothy Leary investigated the imprint phenomena in human beings. He contended that the human nervous system was more sophisticated than that of ducklings and other animals. He established that under the proper conditions, content that had been imprinted at earlier critical periods could be accessed and reprogrammed or re-imprinted. Leary also identified several significant developmental critical periods in human beings. Imprints established during these periods established core beliefs that shaped the personality and intelligence of the individual.

The primary critical periods involved the establishment of imprints determining beliefs about biological survival, emotional attachments and well-being, intellectual dexterity, social role, aesthetic appreciation, and "meta cognition," or the awareness of one's own thought processes. Thus, health problems might stem back to core beliefs and supporting behaviors established during the biological survival critical period, while phobias could have their roots in the emotional well-being period. Learning handicaps might derive from imprints formed during the critical period involving intellectual dexterity, and so on.

[...]Imprints can be significant "positive" experiences that lead to useful beliefs, or they can be traumatic, or problematic experiences that lead to limiting beliefs. Typically, but not always, they involve the unconscious role modeling of significant others. Compare the duck's behavior with human behavior using child abuse as a point of comparison. Research validates that often people who have been abused as children unconsciously get into relationships, as adults, that repeat their childhood experience. For example, often women who have been abused as children marry men who abuse them as adults. Males who were beaten as a child may abuse their own children. If they were beaten by their mothers, they may get into relationships where they are somehow the lesser person. Research shows that women who were beaten by their mothers are apt to be more violent with their own children than those who weren't. Imprints are one explanation of this phenomena. People abused as children can imprint that this is the typical behavior associated with fathers, mothers, husbands or wives. At the time the ducklings were hatching out of the eggs they didn't say, "Gee, that's a strange looking mother; I'd better check things out." Their brains were probably saying, "This is how mothers are,"--human beings do the same sorts of things.

[...]An imprint is not necessarily logical. It's something that's intuitive, and it typically happens at critical developmental periods. In childhood most of us don't have a real sense of self identity, so we pretend we're somebody else, and we often take on the role model--lock, stock and barrel. We can end up like the ducklings that weren't very discriminating about what they would accept as a mother. Who you are as an adult is, in many ways, an incorporation of the adult models you've grown up with. Your model of being an adult has the features of past significant others; features that have been stuck in early ways of believing and behaving that you made a part of yourself at an early age.These beliefs and behaviors emerge when you reach a certain age and are not a child anymore.

[...]The hardest part of changing any belief system is the fact that the imprint is likely to be out of conscious awareness. Your most significant behaviors are usually the ones that are most habitual. Those are the behaviors that you're least consciously aware of.

[Source: Robert Dilts - Beliefs]