Informally, a required field is an input field on a form that must have a non-blank value to be valid.
Conventionally, many flow action forms mark a required field with an orange asterisk (). The image itself is only a label to notify users that the field is required; it does not affect input editing or processing. (The asterisk image is specified in a label, not in the input control.)
On a validate rule, the Required? box produces the runtime error message:
When client-side format validation is enabled, a blank field marked as required is flagged on the browser window when or before the user submits the form.