Definitions for "Authority Site"
Google ranks page links from an Authority Site higher than others. An authority site is a central site in a community determined by counting inbound and outbound links.
a measure of the quality (in the all-powerful opinion of the search engine company) of a given site, gauged by some combination of size, importance, relevance. A link from an authority site to your own is more valuable than just any old site.
a large site that is considered to most important for its keywords