Acquitision report (Direct vs Websites)

In the Acquisition report, I noticed that my website has the following values:500.000 for Direct and 15.000 for Websites.

It seems odd to me to have a value so high for Direct and so low for Websites.

Is there any circumstance where the visitor actually comes from a website but is not tracked accordingly and his visit is counted in the Direct report?

Thanks in advance for your help,
Marco