A datestamp is analogous to a timestamp as a date is to a time. There exist physical devices that serve as datestamps, but usually this refers to data automatically recorded by software. Datestamps are useful for tracking the history of an object. They come in many formats: one could say November 2, 2003; or 02 Nov 2003; or even 11/02/03. I prefer the form 02 November 2003 (Sun), because there is no confusion between the month and the day, the year is four digits, and the day of the week may be used like a redundant check bit. There is often a datestamp command in word processors and text editors. This command will add the current date (either at the time of writing or whenever the document is opened) to the document.
A good example of a combination of datestamp and timestamp is the one at the upper right corner of this writeup.