In software, the term event covers a wide range of architectures and patterns. Generally, it means “Action A triggers action B.” You saw some C# events in chapter 11, such as events in which an entity state changes (section 11.4.4). But this chapter is about another, quite different type of event, which I call an entity event because it is held in your entity classes. Using an entity event is like putting a message in the entity class for someone to read later.
The purpose of entity events is to trigger business logic when something changes in an entity class. In section 12.1.1 I show an example where a change in an address’s details causes the sales tax on a quote to be updated. This example is implemented by detecting a change to the address details and sending an entity event (message) that runs some business logic that updates the sales tax for quotes at that address.