Event : Definition
Data that represents a user interaction that your site or app sends to Google Analytics.
There are two kinds of events: recommended and custom. Recommended events, such as an add-to-shopping-cart event, are common user interactions that you would typically want to track and that Analytics recognizes. Some recommended events are useful for apps/sites in specific verticals such as travel, gaming, or shopping, while other recommended events are useful for all apps and sites. In contrast, custom events are events that you create to represent any arbitrary action that you want to track.