Psychologically speaking, imprinting is when a younger person (typically a child) follows in the footsteps of the
first person they interact with early in their life. It could be their mother, big brother or big sister. When the child views that person as their role model, they have essentially imprinted onto them. The said child fantasizes about being like their role model, being intimate with their role model (e.g. hugging), and willing to do anything they ask. This happens not only in humans but also in animals (e.g.
baby chicks following and copying their
mother duck after hatching).
Going off of that, you could say that in general, imprinting is the act of looking up to a person and viewing them as their idol, often to an excessive and subservient degree.
Imprinting often happens when you crush on someone for
the first time. You just wanna be like them, be with them, and have
everything to do with them. When they're put in the same group as you, you suddenly feel a strong sense of devotion. That is
the essence of imprinting.