noun
Used for a person visiting a patient in a hospital or someone in a similar institutional setting. Often seen in signs and rules about visiting hours.
面会人の受付は午後8時までです。
Visitor reception is until 8 p.m.
面会人は必ずマスクを着用し
Visitors must wear a mask.
訪問者 is a broader term for any visitor, not limited to hospitals or institutions.
Compound of 面会 (meeting, interview) and 人 (person). The exact historical derivation is uncertain, but the word is conventionally associated with institutional visitation.