An event is something that takes place; an occurrence and arbitrary point in time. A significant occurrence or happening. A social gathering or activity.
Individuals define an event's significance subjectively; people actively and retroactively compartmentalize their lives and history in terms of epochs delimited by events considered to be significant.
- In physics (and in some kinds of philosophy), an event occurs at a point in time which can be distinguished because the state of the world changed. Something was different before and after the event. Physics also speaks of event horizons and simultaneity. In Physics and in Science in general, an event may be contrasted with a process, which occurs across intervals, not just at a point on a timeline. An action or relationship may be misunderstood when viewed as an event or single point of focus. Instead, it may help to view it as part of an integrated process.
- In special relativity (and general relativity), an event is a point in the spacetime continuum, i.e. it has a position in space and time.
- In experimental particle physics, an event refers to a set of elementary particle interactions recorded in a brief span of time.
- In probability a possible outcome of an experiment is called an elementary event, while a set of those (a subset of all) is called simply an event (see event (probability theory)).
- In biology one speaks of extinction events.
- In philosophy, one might want to distinguish facts from events, and then between physical events, mental events, and brain events.
Weinberg's Law of Twins states that most of the time, no matter how much effort one expends, no event of any great significance will result.
- In information processing, an event is a change in the properties received by an observer after being transmitted from an object.
- In computer science, an event is a software message that indicates something has happened. See event-driven programming. A number of protocols, such as MIDI, are also event-based.