Authority Site

An authority site is a webpage listing in the SERPs that appears to be authoritative for a number of different reasons.

1. It is listed as number one.
2. The listing contains sitelinks at the bottom of it.

Obtaining authority site status in the SERPs is considered more desirable than getting a double listing.  And, there can be a combination of an authority site and double listing which appears to take up three slots which are even more desirable.