A Person who this Person knows.

“Knowing” is defined as “some form of reciprocated interaction”, not e·g parasocial familiarity from following some·one¦s web feed. But it does not imply friendship or set further constraints on the forms that interaction might have taken. (This is partially because implementation experience has shown formal encoding of concepts like “friendship” to be awkward, especially when both parties are not on the same page regarding it.)