Lookup relationship is a type of field that allows you to link two objects by creating a parent/child relationship. The lookup relationship field allows users to click a lookup (magnifying glass) icon and select a value from a dynamic contextual list. The other object is the source of the values in the list.
The lookup relationship is created on a child object and retrieves and copies data from a parent object.
Lookup filters can be applied in the lookup window to display fewer yet more targeted results. Finally, we can define a dependent lookup relationship on an object to logically match the lookup. A filter will be applied so that two fields point to the same data.
++: This field avoids manual entry of information, and therefore errors, the list of values is updated dynamically, creates a link between two objects (defines a parent and a child)
Example: We want to create a substitute Support Agent field on Cases. Consider then a Case object with a relationship field that points to the User object; But not all users are necessarily competent to handle cases. We will therefore apply a filter on the support User profile.