The Comment column within the FD form enables you to add comments pertaining to the data items defined in the FD form.
This functionality is useful for a developer to maintain a user-friendly definition of the data item, or maybe indicate the uses of a data item that may not be obvious. This can be especially useful for FDs that are imported from another source.
The FD comments can also be inherited by the table definitions if the Inherit Comments from FD tick-box is selected in the Table tab in the Options pane. Imported comments are displayed in the Properties pane when you select a column name in a table definition.