Trigger Custom Events to a Zendesk App

As per the documentation, in

client.on(name, handler, [context])

name: the name of the framework event you want to listen to. 
This can be framework, request, or custom events

How are these custom events triggered?

Use Case: We want to show a popover, based on an activity that happens outside Zendesk to allow an agent to create a ticket for the same.