Your Job Board Token is the unique part of your board's URL on Greenhouse.
For example, Idealist's URL on Greenhouse is boards.greenhouse.io/idealist, so Idealist's Job Board Token is simply "idealist." To learn more about Job Board Tokens on Greenhouse please visit this Greenhouse Help article.
Please note that only US-based organizations can set up a Greenhouse integration. To learn more about integrating your organization's Greenhouse and Idealist account, please visit this Idealist Help Desk article.