Authority sites are websites that are devoted to one specific niche in which there is a very high quality website. The content that is on the site is very well respected by movers and shakers in the industry. An authority site has relevant and useful content that is updated on a regular basis. If you've ever landed on an authority site, you probably were thankful you did because you found the information about the topic that you wanted, and you trusted that it was accurate information.
Authority sites not only publish information that visitors can trust, they curate other trustworthy information for their audience. If you want to create an authority site, you will need to create a lot of accurate, trustworthy, detailed and valuable information and offer it free to your reader. You'll create a variety of different forms of content to inform, instruct, inspire and to encourage interaction. Essentially, you'll be giving away your knowledge, freely. This will encourage the readers to trust you and value any information that you give them.