Page Authority is provided by Seomoz, this metric is at url level - it meaning that each url (page/subpage) have own authority and its a part of domain authority. Both metrics using logarythmic value between 1 and 100, it meaning that more difficult to get value 30 from 20, like from 10 to 20. Higher value of page authority allow for single page get better ranking in search engines.
Here You can quickly check page authority. Enter You url bellow and press CHECK button.