Events

An event is a happening that occurs at a particular time and place of interest to people or systems. In everyday life, events include ceremonies, performances, conferences, sports games, meetings, festivals, and other gatherings. Events are often planned with a program, location, date, budget, and logistics, and they may require permits, safety measures, invitations, and communication with participants. Spontaneous events can also occur, arising from unexpected circumstances or natural phenomena. The significance of an event is usually defined by its attendees, outcomes, or impact on communities, organizations, or cultures.

In probability theory, an event is a subset of a defined sample space representing one or more outcomes of a random experiment. Events can be simple, referring to a single outcome, or compound, formed by unions, intersections, and complements of other events. Probabilities are assigned to events, obeying rules such as the probability of the entire space equaling 1 and the additivity of disjoint events. Common examples include rolling a die and observing an even number, or drawing a card that is a heart from a standard deck. Events help model uncertainty and guide decision making under risk.

In computer science, events are signals or messages that indicate that something has occurred, such as a mouse click, a timer expiration, or a task completion. Event-driven programming uses event handlers or listeners to respond to these occurrences, often asynchronously, enabling interactive software, user interfaces, and reactive systems.

Because events are integral to scheduling and record-keeping, calendars, timelines, and news media organize information around notable events for reference and analysis.