Event Types are the most tricky to understand of the core concepts. We'll do our best to make it simple.
Contacts perform actions in your application like Signing Up or Inviting Users, these are called Events. We receive these Events and parse out who did it and what Account they work for so you can easily follow those things in one of your streams. But we also have another type of Stream called an Event Type Stream and this lets you follow a specific Event Type across all Accounts and Contacts.
Take `Sign Up` as an example. You could follow the `Sign Up` Event Type in a new Stream and pump that into Slack for notifications every time a new user Signs Up to your app. It's that simple.
Within Event Types you'll see two different icons. One is the Event icon, which we use for all Track events like `Signed Up` or `Invited User` and the other is a Page icon we use for page views in your app (Dashboard, Settings, or Stream) and your marketing site (Pricing Page, Contact Page, Blog).
You can mark any event as a "Key Event" this will make that event show up in all your Account and Contact rollups.
To mark an event "key" just go to the event type page and find the toggle at the bottom:
From there you'll see this on all your Account and Contact pages:
In addition, each Account and Contact detail page has a chart to show key event activity over time: