An event is an action or operation that occurs at any given moment in time. Within a web application, an event could be the activation of a new HTTP session.
Events are of great importance in observability they can be used for the real-time analysis of a system's performance or state. An event corroborates the occurrence of an operation within a system at any given time. Events can be derived from arbritrary log data and can be used as a metric that measures the occurrence of selected significant operations, failures, or state changes within a system.