An
app catalog/Apps site is a type of site collection that
is used for storing web parts for your organization's internal
use.
Microsoft has changed the behaviour in SharePoint Online,
so now an app catalog is automatically created the first
time a Global or SharePoint admin clicks on Apps >Open
under 'More features' in the SharePoint Admin center. It
is now called Apps site instead of app catalog.
We have still decided to keep the demo below, as Peter Kalmström
also describes how to reach the Apps site and how it looks
and works. That has not changed.
An
app catalog/Apps site is a type of site collection that
is used for storing web parts for your organization's internal
use. 
