In OOP, a signal to execute code. For example, when you click a button control, you are telling the program to run the code attached to the Click event of the Button object. MS Word and MS Excel macro virii spread by replicating their viral code to the default template during the DocumentOpen event.

A measurable set of points in the measure space of the probability measure.

What this means, in plain English (as opposed to math gibberish) is a set of possible outcomes to which we can assign a probability. For various unpleasant technical reasons we cannot assign probabilities to all sets of outcomes. But we can assign a probability to any set of outcomes which can be described "naturally".

Since events are sets, they're traditionally written inside squiggly brackets.


  • If our probability space is the roll of a fair 6-sided die, then {1 is rolled} and {an even number is rolled} are both events.
  • If our probability space is an infinite series of coin tosses, these are all events (note that each event is a subset of the preceding event):
    • {Infinitely many tosses come up heads}.
    • {There exists an N for which the proportion of heads out of the first n tosses is between 0.4 and 0.6 for all n>=N}.
    • {The proportion of heads out of the first n tosses tends to 0.5 as n tends to infinity}.
  • If our probability space is tomorrow's weather, then {it will rain tomorrow} is an event, but {it will be sunny the day after tomorrow} is not an event (knowing tomorrow's weather does not determine the following day's weather exactly!).

Part of the conceptual switch to relativistic physics includes tossing the concept of a global coordinate frame which fixes every point in time and space uniquely. In order to toss this idea, while retaining a meaningful way to talk about causality, the concept of the event was introduced. An event is a place in timespace where something happens. You can trace the world lines of objects coming into the event, and going out of the event to other events, and in this way preserve causality (the order of events on any object's worldline) but leave time and space coordinates flexible for dilation. Also because different worldlines don't have any global coordinating clock, the dilemma of simultenaity doesn't rear it's ugly head.

E*vent" (?), n. [L. eventus, fr. evenire to happen, come out; e out + venire to come. See Come.]


That which comes, arrives, or happens; that which falls out; any incident, good or bad.

"The events of his early years."


To watch quietly the course of events. Jowett (Thucyd. )

There is one event to the righteous, and to the wicked. Eccl. ix. 2.


An affair in hand; business; enterprise.

[Obs.] "Leave we him to his events."



The consequence of anything; the issue; conclusion; result; that in which an action, operation, or series of operations, terminates.

Dark doubts between the promise and event. Young.

Syn. -- Incident; occurrence; adventure; issue; result; termination; consequence; conclusion. -- Event, Occurrence, Incident, Circumstance. An event denotes that which arises from a preceding state of things. Hence we speak or watching the event; of tracing the progress of events. An occurrence has no reference to any antecedents, but simply marks that which meets us in our progress through life, as if by chance, or in the course of divine providence. The things which thus meet us, if important, are usually connected with antecedents; and hence event is the leading term. In the "Declaration of Independence" it is said, "When, in the cource of human events, it becomes necessary." etc. Here, occurrences would be out of place. An incident is that which falls into a state of things to which is does not primarily belong; as, the incidents of a journey. The term is usually applied to things of secondary importance. A circumstance is one of the things surrounding us in our path of life. These may differ greatly in importance; but they are always outsiders, which operate upon us from without, exerting greater or less influence according to their intrinsic importance. A person giving an account of a campaign might dwell on the leading events which it produced; might mention some of its striking occurrences; might allude to some remarkable incidents which attended it; and might give the details of the favorable or adverse circumstances which marked its progress.<-- events which produced it? -->

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© Webster 1913.

E*vent" (?), v. t. [F. 'eventer to fan, divulge, LL. eventare to fan, fr., L. e out + ventus wind.]

To break forth.


B. Jonson.


© Webster 1913.

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