What Does Direct Traffic Mean In Google Analytics?

Since I’ve been looking this up for my own reasons, I thought I would share my findings. Direct Traffic means of course that there’s NO referrer when the visitor came to the site.

This could be because someone:

• typed in the URL directly in their browser
• used a bookmark in their browser
• clicked a link from an email  with a non-web-based email client (like Outlook)
• clicked a link in a document (PDF, Word)
• clicked a link from within a secure site (https://)
• used a mobile app (which could come from twitter, stumbleupon, email, etc.)
• some JavaScript redirect links may not set a referrer
• some corporate intranets may strip out referrers
• if the user has browser plug-ins to mask their referrer
• some banner/PPC campaigns may not pass a referrer correctly
• The IE browser can sometimes be problematic & not send a referrer under certain conditions

Has anyone heard of any other reasons traffic would be identified as direct traffic in Google Analytics?