Traffic is broken down into channels to best determine and segment traffic activities based on their source. This guide discusses in detail and addresses some common trends on different traffic types and how they interact with a website.
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The primary report within Google Analytics is User Acquisition
This graph shows you the total amount of traffic over the date range specified. Below the graph is a table where the traffic is segmented into channels. Each channel is a group of traffic from a different source.
Traffic that is unable to be classified by the source from which it came. This can happen when someone types or pastes your URL to visit your site directly, clicks a bookmark or otherwise ends up on your website by clicking a link that Google Analytics can't see (such as when someone uses an incognito window). This is also use when for other reasons Google is unable to classify the traffic source. Refer to 
Common Fluctuation Causes of Traffic Types for details on investigating direct traffic.
Organic Search refers to traffic that comes from search but from the non paid ad portion of the search results. While the vast majority of this comes from Google Search, typically you will see supplemental Organic Search traffic from places such as Bing, DuckDuck Go, etc.
Paid Search traffic is traffic coming from PPC efforts from networks such as Google, Bing, Facebook, etc. While Google and Bing easily allow for auto-tagging, PPC efforts from Facebook will require the usage of UTM Tags.
Display traffic is traffic that comes from paid advertising efforts, however this is typically from Google Display Network/Remarketing efforts where people see ads while browsing the internet instead of Search traffic where someone was actively searching for a product or service.
This is traffic that comes to your website via Social Media Channels such as Facebook, Instagram, Pinterest, etc. One reason why UTM Tagging is crucial for Facebook paid efforts is because otherwise, Google Analytics will instead tag traffic from these efforts as Social traffic.
Referral traffic is traffic where someone got to your website from clicking on a link from another website. In other words, this would exclude traffic from sources such as Social Media, E-Mail, etc.
This is a special channel that can easily be confusion. You may send out newsletters that have links to your website but never see traffic classified in the Email channel. This is because Email traffic can only be classified properly by using UTM codes (see About UTM Codes ) Without UTM Codes all email traffic will typically be classified as 'Direct Traffic'.
You can use a QR code on a postcard, sticker, or sign that can take a user to a website. If you do not use a UTM code the visit will be classified as 'Direct' (see above) but with UTM codes you can classify visits via physical medium in Google Analytics as well.
You may notice a significant amount of direct traffic, or perhaps the traffic attributed to the email channel missing entirely. Refer to Common Fluctuation Causes of Traffic Types
About UTM Codes Granting Access in Google Analytics SEO Listing Sync and Reputation Management Index Note: For open questions - use the 'Request an Update' tool at the bottom for notes on future updates needed.
