Adding a Reference field on table A that points to table B, creates a relationship that ServiceNow can understand. This allows you to add a related list on records in table B, that displays the records from table A that are linked to it.
Creating a M2M table via the sys_m2m relationship definition table also creates a relationship that ServiceNow can understand. Because of this, you can add a related list on either of the two tables linked by the relationship, to show related records from the other table.
If you want to define a more complex relationship, however, ServiceNow allows you to do that as well! Let's explore an example of defining a custom relationship for tickets generated from.
Requests have a sort ...
