Merge fields are named 'Tokens/placeholders' inside the Greenhouse recruitment system.

You can access the 'tokens/merge fields' inside email templates. The supported tokens depend on the email type.

When you add a tag to an email template, it inserts it in the format that we need, which is some value surrounded by {{ }} as shown below:
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You need to copy the tags and don't necessarily have to implement them or add them to your existing email templates. Greenhouse provides a complete list of standard tokens in this article.

Custom tokens can be found inside your Greenhouse system; go to this article to learn more.