mount is used to mount another application (basically rack application) or rails engines to be used within the current application
mount SomeRackApp, at: "some_route"
Now you can access above mounted application using route helper
But if you want to rename this helper name you can do it as:
mount SomeRackApp, at: "some_route", as: :myapp
This will generate the
myapp_url helpers which can be used to navigate to this mounted app.