Use a date phrase when you don’t know the exact date, but have some information which gives helpful information about it. For example, if all you know about a person’s death is that “it occurred less than 2 months after his wife died”, you can record that note as a date phrase.
If you wish to do so, you can optionally also provide a date, as your interpretation of the date phrase.
See Simple Date Fields for help on the date fields.
With fact dates (dates of events or attributes, displayed in the Facts tab of the Property Box), you can optionally also enter a separate sort date.