A person who comes to visit a place, home, or office. Slightly formal; in casual contexts, お客さん or 訪問者 may be more common.
There are many visitors today, so I can't get much work done.
The parking lot for visitors is over there.
来訪者 and 訪問者 both mean 'visitor' in formal contexts, but 来訪者 is slightly more literary and often used in written announcements.
Compound of 来訪 (raihō, 'visit') + 者 (sha, 'person'). The kanji 来 means 'come', 訪 means 'visit', and 者 means 'person'.