The list of item types found here (https://developers.arcgis.com/rest/users-groups-and-items/items-and-item-types/) does not appear to be accurate. Map Service, Feature Service, etc. note they are specifically for ArcGIS Server services which usually means AGOL works differently. However, this is not the case as AGOL uses these when filtering for Map image layers, Feature layers, etc.
Map Service also links to ArcMap documentation which should be updated by this point.
