- A case is a project linked to a service or item purchased by a customer -- it is linked to an account and require actions to achieve an outcome by a certain deadline. This action may require document sharing, access to knowledge base, communication with team members...

- A campaign is a project linked to a service or item to be purchased by a costumer...

- A service is a project linked to a contract with a customer...

Those are project items that shares common characteristics. They can be segregated under different view or layout but at their core they are identical objects.