Third Party Organisations are the organistaions to which employee deductions may be paid. For Australia, this includes Superannuation companies to which company superannuation contributions are paid as well as employee deductions and salary sacrifices.
The code itself can be any 10 alphanumeric characters. You will find that lower case characters you type will be translated automatically to upper case. If adding a Superannuation company, make the code the same as the SuperFund property in the pay item setup form for each of the company's superannuation contribution pay items.