A custom role is a collection of rights that you define, and then easily give to others. To create a custom role, you need to be Access manager and have the rights that should be part of the role.
You create a custom role under profile → others with rights if you choose a person or click add new person. Click Has these roles, and then select +Add new role.
By editing a custom role, you can eitehr add or remove services from the role, or delete the role itself.