The organisation this user works for. You can add a specific company that the service agent works for OR you can select to make them a 'Global Agent' where they aren't linked to a specific company. Service agents linked to a specific company will not be able to be added as a contact to a work item belonging to a different company. 'Global Agents' agents have much more flexibility - they can be linked to any work item, regardless of company, letting them send and receive communications from them, and they can also be added to any team, regardless of the company the team leader is linked to. This is particularly useful when your organisation has different operations set up as separate customers.