Refers to a person passing by on foot, often in contexts like traffic, streets, or public spaces. Similar to 通行人, but 通行者 can sound slightly more formal or official.
See also: 通行人
There are many pedestrians on this road, so cyclists need to be careful.
The police questioned passersby to find witnesses to the accident.
Compound of 通行 (passage, traffic) and 者 (person). The exact historical derivation is straightforward; the word follows a common pattern for forming agent nouns.