Hidden field for administrator only

We need to add a data entry back end field (such as "paid by check") that people do NOT see when they enter their data into our forms but that we can see when we run reports. How do we accomplish this?  Thank you.

You can use a hidden field that your users will not see. But it will be visible in a report.

For example this form:

https://form.jotformpro.com/72354918927973

Will populate the hidden field, but its only visible to an administrator: