Answer
The relationship between Contact and Account is actually a lookup relationship. However, when an Account is deleted, all related Contacts are also deleted. From this perspective, it behaves like a master-detail relationship. A Contact can still be created without an associated Account, which is a feature of a lookup relationship. Therefore, we can also call it a hybrid relationship, even though it is technically a lookup. Additionally, we cannot use roll-up summary fields on the parent object since it is not a true master-detail relationship.