An event is a type of action or occurrence in Java that is triggered by another type of action or occurrence. The click event is triggered when a user hits a button on a web page, for example. Some events are significant because they occur frequently and can have a significant impact on how the program is carried out. The occurrence of a user clicking a button on a web page, for example, is significant because it can initiate a chain of actions that the user desires. Other events, like the beginning or conclusion of a program, are less common but significant because they signal the start or end of the program's execution. In Java, there are a number of different ways to handle events. One way is to use the adapter pattern. Another way is to use the observer pattern.