event(1) An action or occurrence detected by a program. Events can be user actions, such as clicking a mouse button or pressing a key, or system occurrences, such as running out of memory. Most modern applications, particularly those that run in Macintosh and Windows environments, are said to be event-driven, because they are designed to respond to events.
(2) ITIL defines an event as "any detectable or discernable occurrence that has significance for the management of the IT infrastructure or the delivery of IT service and evaluation of the impact a deviation might cause to the services." (ITIL Service Operation book, Page 35).