These events describe changes in AWS services, example: EC2 instance is started
EventBridge is a newer system replacing CloudWatch Events. It can perform the same functionality, in addition it can handle events from third-parties and custom applications
Both of the services operate using an event bus. Both have a default event bus
In CloudWatch Events there is only the default event bus, which is explicit and it is not exposed to the UI
In EventBridge we can have additional event buses
In both systems we create rules matching incoming events, or we have scheduled based rules
Events themselves are JSON objects, including for example which EC2 instance changed state, in what state changed into as well as other things such as date and time