Domain and page authority are phrases used by SEOMoz to assess the competitivness and value of a site. It is basically trying to emulate Google PR and ranking algorithm but as no one knows how this really works (apart from G) they have done the best they can which is pretty good in my opinion and called it DA and PA.

I think it gives you a more thourough view of a website and particurlarly a page when linkbuilding.

Domain name authority is determined by the number of links pointing back to the domain, also the page authority otherwise known as PR, you can check this on opensiteexplorer dot com.
You can enhance your page rank and domain authority by link building through forum posting, blog commenting, article marketing.

Domain and Site authority are one of the phase of analyzing the base URL and its corresponding paths.

Domain authority takes into account numerous factors, age of the domain is important as is the DA of sites linking to you. I have an SEOMoz account and find this a great tool for measuring your sites improvement and competition analysis.

The group of computer, which connected by Internet with same network. then all system are define by particular address, these called domain. and site authority means suppose i am a admin, and i give the rights to access my site to another person thats called site authority.