Definition
Event
An event is a set of outcomes chosen from a chance experiment.
What it means
First list the possible outcomes. Then ring the outcomes that count for the question. That ringed group is the event. An event may contain one outcome, several outcomes, every outcome, or no outcomes.
Remember it
Draw a ring around all the outcomes that count; the ringed set is the event.
Example
A spinner has five equal sections numbered 1 to 5. The event “spin a number greater than 3” is the set {4, 5}. If the spinner lands on 4 or 5, the event occurs.
Watch for
The number 4 by itself is one outcome. The event “greater than 3” contains two outcomes: 4 and 5.
Common mix-up
An event is not a party or simply “what happened”; in probability it is the selected set of outcomes before or after a trial.
Exact meaning
For a stated sample space, an event is any set of outcomes. The event occurs when the result of the trial is one of the outcomes in that set.