What is imprinting?
In regards to animal behavior, imprinting occurs when, early in an animal's life, the animal forms an attachment to another organism and learns the characteristics of that organism.
Imprinting likely has a critical period during which the young organism will attach to another. The organism will then learn behavior from whatever it has imprinted on. It will also learn to be sexually attracted to that organism.
For example, arguably one of the most famous examples of imprinting occurred when birds imprint onto humans. A clutch of goslings imprinted onto the human, Konrad Lorenz, and followed him around as if he was their mother (Hess, 1958).
Here's a good article from PBS on the science of imprinting .