Out-of-the-box event tracking
In Universal Analytics, events are user interactions measured independently from a web page or screen load. Downloads, link clicks, form submissions, and video plays are often measured as events. Events in Universal Analytics have a Category, Action, Label and sometimes a Value, and are displayed with these fields in your Analytics reports.
In Google Analytics 4 properties, events are user interactions with a website or app that can be measured concurrently or independently from a webpage/screen load. Examples of events include page views, button clicks, user actions, and system events.