When creating a field in a GoCanvas App, you have the option to disable a field's Mobile Visibility, meaning the person filling out the Submission won't see it in their App.
Why would I want to create a field, only to hide it? There are plenty of fields that perform valuable functions in your App, but don't necessarily need to be shown. Sometimes they clutter up the App and you'd like to keep it clean and concise for your users.
A lot of the time, they perform background work that's essential to populating other fields (think about the multiple Calculation fields it might take to achieve one final numeric output that's worth making visible). Check out this example of a common use case, where you utilize a multitude of Calculation fields to achieve one field that displays someone's current age based on their birthday and the current date.
In the App Builder, you'll find this setting under the More section of your Field Settings.