Calling ArcGIS Online a 'portal' is confusing, because 'Portal' (capital P) is a product in its own right. Under current Esri nomenclature ArcGIS Online is a 'portal' (lower case p) but is not Portal (upper case P). Clear as mud?
Instead, why not call ArcGIS Online a 'gateway', 'door', 'gate' or something else? Call it anything except a 'portal'. Then we can say for example:
ArcGIS Online is a gateway.
Portal is a gateway.
That is so much simpler and causes way less confusion.
