Imprinting is when a werewolf imprints on another human being or (werewolf.) It is more potent, more intense than regular love. It is vividly described in detail in the Twilight books. Specifically in Eclipse. Jacob Black describes it as gravity moving, she's the one that holds you not anything else. She is the focus. Nothing else matters but her.You will defy anyone for that person, do anything for that person.
It is strongly suggested that once a werewolf imprints, the imprintee has no choice but to be with that person. But it is also said that the relationship between a werewolf and his imprint can vary between a physical one and a more brotherly and best friend relationship.
The only known werewolves known to have imprinted are: Sam Uley, to Emily Young; Quil Ateara with Claire Young (Emily's niece.) Though that relationship will not become physical until Claire comes of age. Paul, to Rachel Black (Jacob Black's sister.) Jacob Black to Renesmee Cullen (daughter of Edward Cullen and Bella Swan.) and Jared to Kim Conweller It is not known if the other werewolves have imprinted.