noun
visitor; observer; person on a tour
Refers to someone visiting a place such as a factory, school, laboratory, or facility for observation or a tour.
工場の見学者はヘルメットを着用してください。
Visitors to the factory must wear helmets.
来週、学校に見学者が来る予定です。
Some visitors are scheduled to come to the school next week.
訪問者 is a more general visitor, often to a person's home or office, while 見学者 specifically implies an observational or educational visit.
Compound of 見学 (けんがく, 'observation, study tour') + 者 (しゃ, 'person').