Relates associate data in different tables, and can be defined for tables that belong to different workspaces. Relates display information from related tables in the Identify dialog box.
Features cannot be symbolized based on related data. The results from a query on a related table cannot be automatically applied to the source layer. You can use joins to accomplish these tasks, as long as there is one-to-one or a many-to-one relationship between the tables.
For more information, see Desktop Help > Contents > ArcMap > Working with tables > About joining attribute tables.