FIELD_PROMPT is a 30 character field which is used throughout the application to provide the ability for users to give a field a prompt. 

One usage of the field is for distribution segments. When the Distribution Editor button is invoked on various forms (e.g. [IDPP], [IDPS], [IDJB], [IEAS], [IPTR], [IPPH], etc.), the value in this field is used as a side label for the segment to be entered.

Another usage for this field is with user defined fields in [IMUF]. When a user defined field is created the user must supply a 'prompt' so that the end user understands what the udf is for.