Refers to a person who enters a place without permission, often with a nuance of forceful or unwelcome entry. Slightly formal or literary.
Late at night, an intruder came into the house.
He was treated as a trespasser on the private property.
From 闖入 (ちんにゅう, 'intrusion, forcing one's way in') + 者 (しゃ, 'person'). 闖入 is a kango compound using the character 闖 (to rush in, to burst in).