Other forms: bystanders
A bystander is somebody present at an event but taking no part in it. Watching, and not involved.
News reports use it constantly, and an innocent bystander injured in an incident is a fixed phrase. Psychology has the bystander effect, the well-documented finding that the more people witness an emergency, the less likely any one of them is to help, since everybody assumes somebody else will. Bystander intervention training exists precisely to counter that. The word is neutral, but the phrase standing by carries a hint of failing to act.
1nounbystanderA person present at an event without taking part.
“Several bystanders had filmed the whole thing.”
From by- + stander. Compare passerby.
Etymology from Wiktionary, CC BY-SA