I want to know about web page authority, my 20 days old website page authority is 27. is it good.
A quick search found this explanation, which seems to cover it nicely:
Page authority is a metric, developed by SEOMoz, to predict the ability for a specific page to rank in search engines. Page authority uses a 0 to 100 logarithmic scale. A high Page authority score means your page has the potential to rank well in search engine results.
If you want more information, try http://moz.com/learn/seo/page-authority
It’s the same as Google defined the PageRank… only SEOmoz calls it Page Authority… if you ask me 
I think it is a phrase used to help convince you of the importance of search engine optimization, and the use of specific marketing tools to track your progress. I believe these tools cost $100/month. 