A person who, although present at some event, does not take part in it; an observer or spectator.

plural of bystander

Standing nearby; having the role of bystander.

(psychology) The phenomenon that someone is less likely to help another if other potential helpers are present than otherwise.

a person who, although present at some event without taking part in it, is affected by it deleteriously

plural of bystander effect

plural of innocent bystander

The role of being a bystander, not taking any active part.

(rare) Of, or characteristic of a bystander.