The field description allows you to add additional information for the data collector or user when they are entering data into a field so that they know exactly what kind of information they should enter to the field.
The description is available for all field types except Section, Repeatable, and Label.
While this configuration option accepts large chains of text, it is recommended that you keep them short but descriptive enough for the data collectors or users to understand.
This is visible during form entry through the small info icon in the upper-right corner for each field that has a description configured.
You can use this to display guidelines or instructions to mobile users on how to capture data for the field — like examples, requirements, and longer descriptive questions to help guide the data collector or user.