A safety event is any event in which safety played a role, either positively or negatively.
You can be “part” of a safety event because your actions directly or indireclty led to it. You can observe a safety event as a colleague, a bystander, teamleader, supervisor, or subordinate.
Usually a safety event is associated with something negative, e.g. an accident or incident. Even low-severity incidents (sometimes called ‘routine events’ because they happen all the time) are of relevance.
But quite often safety events can be regarded as positive. Something went extraordinarily well. Somebody stopped a routine event from developing into a major accident.