Triggers are a special type of directive prefixed with an “@” that allow your elements to be bound to defined animations in the @Component decorator. Each trigger is represented by a defined animation trigger and each trigger can support many states.
These Plunkr demos don't seem to work anymore...
You can get them going again by replacing the zone.js reference with this one: "https://unpkg.com/zone.js@0.6.23?main=browser"