• Direct Traffic: all those people showing up to your Web site by typing in the URL of your Web site coming or from a bookmark. Some people also call this "default traffic" or "ambient traffic."
• Referring URLs: other Web sites sending traffic to you. These could be as a result of your banner ads or campaigns. These could be all those blogs or affiliates who link to you.
• Search Engines: Google, Yahoo, MSN, Ask, others. This bucket will include both your organic as well as your paid (PPC/SEM) traffic, so be aware of that.
• Other: These include campaigns you have run, e-mail, direct marketing and so on.

See also "Web Analytics Primer: Five Metrics Demystified" on Ecommerce-Guide.com.

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Web Analytics Primer: Five Metrics Demystified
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