What are the requirements for a 'standardised page' as used in Writer word count?

When I do a word count in Writer, it counts words and characters with/without spaces, but alsop calculates ‘standardised pages’. What kind of page is that: a book page, an A4 page, US letter, or…?

As explained in this Google groups answer, a “standardised page” is determined by basic division (by 250) of the total number of words in the manuscript, rather than a specific page size. It has been used for many years by publishers to roughly indicate the number of pages a work will result in.