Hi Foura,

 Relationship is something which can be created in between two tables based on custom evaluation/conditions as per our requirement.

Once you create a relationship definition between table X and table Y (based on some conditions), you can now be able to configure the "Related List" under on table record of X with the table records of Y &/OR vice versa.

Thanks,
Saikiran Guduri (NOW)
Associate Certificate Engineer | ServiceNow Store Apps
(Please mark the answer as correct answer/helpful/accept the solution if it helps)