It's a loosely coupled relationship among Salesforce objects. In the Lookup relationship, both parent and child have their sharing setting and security controls, which means if a parent record gets deleted, then child records remain in the system.
Let's see the party and the people objects. For example, the below figure provdes a visual representation of the Lookup relationship between the party and people objects.
In this diagram, the party object record has been deleted, but the people record is still available. This relationship between objects is Lookup relationship.
