The channel overview breaks down the traffic source information which tells you the different ways that people can find your website.
Visitors who are considered organic find your website after using a search engine like Google or Bing and click on a non-paid search result.
Direct traffic is most often the result of a user entering the URL into their browser or using a bookmark to directly access your website. This channel often accounts for existing patients, direct referrals from other physicians or other offline forms of advertising.
Visitors that find your website from a source outside of a search engine would be considered referral traffic. When someone clicks on a hyperlink to go to a new page on a different website, Google sees that as referral traffic. Example: new stories, social media, review sites, hospital websites
Local traffic is a result of someone that interacted with your site via an online directory or local listing. This also includes your Google My Business listing.
This is the traffic that you purchase via AdWords or pay-per-click ads. These listings typically show above the non-paid results and are indicated as ads to the end-user.