This is the concept of specific associations in which many souls form special relationships during one or more lifetimes in order to gain certain experiences. The term is often quoted in the Seth Speaks books.
There are many forms of counterparts, both loosely and closely aligned. The term has been used for the associations within group soul consciousness, reincarnation, incarnating experiences between certain souls, and the psychic families of consciousness whose characteristics focus on specific social functions within the human experience.
Telepathic impressions pass more easily and quickly between counterparts. Certain memories of another counterpart may appear as fantasies or in dreams.