The classic example of this in my mind is the relationship between Lexus and Toyota. At least in the United States, Lexus is not presented as "Lexus... by Toyota". From a newcomer's perspective, it is a fully independent entity.
For Toyota, Lexus was targeted at a specific market segment, sales to which might have been adversely impacted by using the Toyota name.
The term I thought of for this was "house brand", but googling suggests that term's meaning is generally confined to supermarket generics like "Sam's Choice".
Can someone please help me properly name this brand relationship?