noun
Refers to a person from outside a group, community, or region; can be neutral or carry a slight sense of unfamiliarity.
村では外来者を珍しがる。
In the village, they find strangers a novelty.
外来者の立ち入りは禁止されている。
Entry by outsiders is prohibited.
訪問者 specifically means 'visitor' in the sense of someone who comes to visit a place or person, without the 'outsider' nuance.
Compound of 外来 (がいらい, 'coming from outside') + 者 (しゃ, 'person').